U.S. patent number 7,817,281 [Application Number 11/702,320] was granted by the patent office on 2010-10-19 for tuning optical cavities.
This patent grant is currently assigned to Palo Alto Research Center Incorporated. Invention is credited to Michael Bassler, Peter Kiesel, Oliver Schmidt, Uma Srinivasan.
United States Patent |
7,817,281 |
Kiesel , et al. |
October 19, 2010 |
Tuning optical cavities
Abstract
An inhomogeneous optical cavity is tuned by changing its shape,
such as by changing reflection surface positions to change tilt
angle, thickness, or both. Deformable components such as elastomer
spacers can be connected so that, when deformed, they change
relative positions of structures with light-reflective components
such as mirrors, changing cavity shape. Electrodes can cause
deformation, such as electrostatically, electromagnetically, or
piezoelectrically, and can also be used to measure thicknesses of
the cavity. The cavity can be tuned, for example, across a
continuous spectrum, to a specific wavelength band, to a shape that
increases or decreases the number of modes it has, to a series of
transmission ranges each suitable for a respective light source,
with a modulation that allows lock-in with photosensing for greater
sensitivity, and so forth. The optical cavity can be a linear
variable filter fabricated on the photosensitive surface of a
photosensing component such as a photosensor array or a
position-sensitive detector.
Inventors: |
Kiesel; Peter (Palo Alto,
CA), Schmidt; Oliver (Palo Alto, CA), Bassler;
Michael (Menlo Park, CA), Srinivasan; Uma (Mountain
View, CA) |
Assignee: |
Palo Alto Research Center
Incorporated (Palo Alto, CA)
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Family
ID: |
39676118 |
Appl.
No.: |
11/702,320 |
Filed: |
February 5, 2007 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20080187011 A1 |
Aug 7, 2008 |
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Current U.S.
Class: |
356/454;
356/519 |
Current CPC
Class: |
G01J
3/26 (20130101); H01S 3/08081 (20130101); H01S
3/105 (20130101) |
Current International
Class: |
G01B
9/02 (20060101) |
Field of
Search: |
;356/454,519 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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WO 95/20144 |
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Jul 1995 |
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WO |
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2006013360 |
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Dec 2006 |
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WO |
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Primary Examiner: Lee; Hwa S. A
Claims
What is claimed is:
1. A method of using an optical cavity with a sensor component, the
optical cavity having a changeable shape and with an analyte region
in the optical cavity that can contain analyte; the method
comprising: tuning the optical cavity by changing its shape through
a sequence of two or more optical cavity shapes, each with
laterally varying optical thickness; providing output light with a
laterally varying intensity distribution that depends on the
optical cavity's shape and on analyte in the analyte region, and
wherein the optical cavity operates as an inhomogeneous optical
cavity; and operating the sensing component such that the act of
operating including at least one of: providing feature signals
indicating shape of one or more of the deformable components;
providing feature signals indicating distance between the first and
second light-reflective components; and capacitively sensing
distance between electrodes.
2. The method of claim 1 in which the act of tuning is performed
before the act of operating.
3. The method of claim 2 in which the act of tuning determines a
photon energy range in which the optical cavity transmits light;
the output light being within the photon energy range.
4. The method of claim 2 in which the act of tuning changes the
number of modes in which the optical cavity provides output
light.
5. The method of claim 1 in which the act of tuning and the act of
operating are performed concurrently.
6. The method of claim 5 in which the act of tuning comprises:
continuously changing the optical cavity's shape while performing
the act of operating.
7. The method of claim 6, further comprising: photosensing the
output light at a photosensitive surface; the act of tuning further
comprising: modulating the optical cavity's shape at a frequency to
perform a lock-in operation.
8. The method of claim 5 in which the act of tuning comprises:
incrementally changing the optical cavity's shape while performing
the act of operating.
9. The method of claim 1 in which the act of tuning and the act of
operating are performed alternately.
10. The method of claim 9 in which the act of operating includes a
series of operations during each of which the optical cavity
receives input light from a respective light source; the act of
tuning including, after each operation in the series, an act of
changing the optical cavity's shape for a next operation in the
series of operations.
11. The method of claim 1, further comprising: providing input
light to the optical cavity and photosensing output light provided
by the optical cavity in response to the input light to obtain
sensing results; the act of providing input light and photosensing
output light comprising: providing tuning signals causing the
optical cavity to change through the sequence of two or more
optical cavity shapes; for each shape, the photosensed output light
having a respective laterally varying intensity distribution; the
sensing results including information resulting from the laterally
varying intensity distribution.
12. The method of claim 11 in which the act of providing tuning
signals further comprises: providing a sequence of tuning signals
so that the sensing results indicate a derivative of one of
absorption and dispersion with respect to wavelength.
13. The method of claim 11 in which the photosensed output light
includes a light spot on a photosensitive surface; the act of
providing tuning signals comprising: providing tuning signals that
cause the optical cavity's output energy function to vary
periodically with a constant frequency; in response, the light spot
moving periodically over the photosensitive surface with the
constant frequency.
14. The method of claim 1 in which the act of tuning the optical
cavity comprises: changing the optical cavity's shape
continuously.
15. The method of claim 1, further comprising: transferring analyte
into, through, or out of the analyte region in the optical
cavity.
16. A method of using a tunable optical cavity and a photosensing
component, the optical cavity having a changeable shape, the
photosensing component having a photosensitive surface; the method
comprising: tuning the optical cavity by modulating its shape with
a constant frequency, causing the optical cavity's output energy
function to vary periodically with the constant frequency;
providing input light to the optical cavity; the optical cavity
responding to the input light by providing output light on the
photosensitive surface, the output light including a light spot; in
response to the periodically varying output energy function, the
light spot moving periodically over the photosensitive surface with
the constant frequency; with the photosensing component,
photosensing the output light to obtain photosensing results; using
the photosensing results to obtain a differential quantity
indicating the light spot's position on the photosensitive surface;
and performing a lock-in operation to increase the precision of the
light spot's position as indicated by the differential
quantity.
17. A method of using a system that includes: one or more sensing
components; a tunable optical cavity device; and a photosensing
component having one or more photosensitive surfaces; the method
comprising: providing tuning signals to the tunable optical cavity
device that cause the optical cavity to have a sequence of two or
more shapes, the optical cavity's shape changing between first and
second shapes in the sequence; each of the first and second shapes
having laterally varying optical thickness such that the optical
cavity operates as an inhomogeneous optical cavity when it has one
of the first and second shapes; operating the tunable optical
cavity device while the optical cavity has the first and second
shapes; the act of operating the tunable optical cavity device
including: operating the optical cavity with first and second
laterally varying energy output functions that depend on the first
and second shapes, respectively; the first and second laterally
varying energy output functions being different; and operating the
optical cavity with the first and second laterally varying energy
output functions to provide respective output light, the respective
output light of the first and second laterally varying energy
output functions having first and second laterally varying
intensity distributions, respectively, on the photosensitive
surfaces; operating the photosensing component to provide, in
response to the respective output light of the first and second
laterally varying energy output functions, respective sensing
results including information resulting from the first and second
laterally varying intensity distributions, respectively; and
operating the sensing components to sense a feature of the relative
position of the first and second light-reflective components and
provide feature signals indicating the sensed feature; the tuning
signals being provided in response to the feature signals.
18. The method of claim 17 in which the tuning signals cause the
optical cavity to have the sequence of shapes by doing at least one
of: changing a tilt angle; and changing an optical distance.
19. The method of claim 17 in which the tunable optical cavity
device has an exit surface at which it provides output light, the
photosensing component being connected to the exit surface; the
optical cavity providing the respective output light of the first
and second laterally varying energy output functions on the
photosensitive surfaces through the exit surface; the act of
operating the photosensing component including: operating the
photosensing component to photosense the respective output light of
the first and second laterally varying energy output functions
received through the exit surface.
20. The method of claim 17 in which the system includes a
processor, the act of providing the tuning signals including:
operating the processor to provide the tuning signals based on the
feature signals and on calibration data.
21. The method of claim 17 in which the tunable optical cavity
device includes first and second light-reflective components, the
act of operating the sensing components including: operating the
sensing components to sense distance between the first and second
light-reflective components.
22. A method of using an optical cavity device that includes: a
light-transmissive region that includes an analyte region; first
and second light-reflective components with the light-transmissive
region between them; each of the light-reflective components
reflecting light into the light-transmissive region; and a set of
one or more tuning structures; one or more of the tuning structures
in the set each including: respective first and second electrodes;
and a respective deformable component between the respective first
and second electrodes; the method comprising: for each of a subset
of one or more of the tuning structures, providing respective
electrical tuning signals to at least one of the respective first
and second electrodes, the respective electrical tuning signals
causing deformation of the respective deformable component; the
respective electrical tuning signals provided for the subset of
tuning structures together causing the first and second
light-reflective components to move into a first position relative
to each other; in the first position and with analyte in the
analyte region, the first and second light-reflective components
having laterally varying optical distance between them; while the
first and second light-reflective components are in the first
position, operating the light-reflective components and the
light-transmissive region as an optical cavity with analyte in the
analyte region, the optical cavity being inhomogeneous due to the
light-reflective components' being in the first position relative
to each other; the analyte affecting the optical cavity's output
light; and changing a tilt angle between the first and second
light-reflective components.
23. The method of claim 22 in which the respective electrical
tuning signals cause deformation of the respective deformable
component by causing at least one of: deformation of dielectric
elastomer material in the deformable component in response to an
electrostatic field between the respective first and second
electrodes; deformation of nonmagnetic elastomer material in the
deformable component by electromagnetic attraction or repulsion
between the respective first and second electrodes; and expansion
or contraction of piezoelectric material in the deformable
component in response to electrical signals received through the
respective first and second electrodes.
24. A method of using a tunable optical cavity structure that can
operate as an optical cavity, the tunable optical cavity structure
including: first and second inward reflection surfaces; a
light-transmissive region between the first and second inward
reflection surfaces; an analyte region that can contain analyte
within the light-transmissive region; and a set of one or more
tuning structures; the method comprising: operating the set of one
or more tuning structures to cause relative movement of the inward
reflective surfaces at a modulation frequency; while the inward
reflective surfaces have movement relative to each other at the
modulation frequency, operating the tunable optical cavity
structure as an optical cavity with analyte in the analyte region,
the analyte affecting the optical cavity's output light, the
optical cavity's output light further changing periodically at the
modulation frequency and further includes a laterally varying
intensity distribution; and changing a tilt angle between the first
and second inward reflection surfaces.
25. The method of claim 24 in which the act of operating the set of
tuning structures comprises: operating the tuning structures to
continuously change the shape of the light-transmissive region.
26. The method of claim 24, further comprising: transferring
analyte into, through, or out of the analyte region.
27. A method of using an optical cavity device that includes: a
light-transmissive region that includes an analyte region; first
and second light-reflective components with the light-transmissive
region between them; each of the light-reflective components
reflecting light into the light- transmissive region; and a tuning
structure that includes: one or more deformable components; and one
or more sensing components; the method comprising: operating the
sensing components to provide feature signals; based on the feature
signals, causing deformation of at least one of the deformable
components, the deformation causing the first and second
light-reflective components to move among a set of positions
relative to each other; and while the first and second
light-reflective components are in at least one of the set of
positions relative to each other, operating the light-reflective
components and the light-transmissive region as an optical cavity
with analyte in the analyte region, the analyte affecting the
optical cavity's output light, the analyte-affected output light
including infoimation about one or more optical characteristics of
the analyte; the act of operating the sensing components including
at least one of: providing feature signals indicating shape of one
or more of the deformable components; providing feature signals
indicating distance between the first and second light-reflective
components; and capacitively sensing distance between
electrodes.
28. A method of using an optical cavity with an analyte containing
region with a changeable shape; the method comprising: tuning the
optical cavity by modulating its shape at a modulation frequency
such that a tilt angle of the optical cavity is changed; and
operating the optical cavity to provide output light from the
analyte containing region with a laterally varying intensity
distribution that depends on the optical cavity's shape; the act of
tuning and the act of operating being performed concurrently such
that the laterally varying intensity distribution changes at the
modulation frequency.
29. The method of claim 28, further comprising: photosensing the
output light at a photosensitive surface; the act of tuning further
comprising: modulating the optical cavity's shape at the modulation
frequency to perform a lock-in operation.
30. The method of claim 29 in which the act of modulating the
optical cavity's shape further comprises: causing an output energy
function of the optical cavity to vary periodically with the
modulation frequency; the act of operating the optical cavity
further comprising: providing input light to the optical cavity;
the optical cavity responding to the input light by providing
output light on the photosensitive surface, the output light
including a light spot; in response to the periodically varying
output energy function, the light spot moving periodically over the
photosensitive surface with the modulation frequency; the act of
photosensing the output light comprising: photosensing the output
light at the photosensitive surface to obtain sensing results; the
method further comprising: using the sensing results to obtain a
differential quantity indicating the light spot's position on the
photosensitive surface; the lock-in operation increasing precision
of the light spot's position as indicated by the differential
quantity.
31. The method of claim 28 in which the act of tuning the optical
cavity comprises: providing tuning signals causing the optical
cavity to change through a sequence of two or more optical cavity
shapes; the method further comprising: photosensing the output
light at a photosensitive surface to obtain sensing results; for
each shape in the sequence, the photosensed output light having a
respective laterally varying intensity distribution; the sensing
results including information resulting from the laterally varying
intensity distribution.
Description
This application is related to the following applications, each of
which is hereby incorporated by reference in its entirety:
"Chip-Size Wavelength Detector", U.S. patent application Ser. No.
10/922,870, now published as U.S. Patent Application Publication
No. 2006/0039009; "Sensing Photon Energies Emanating From Channels
or Moving Objects", U.S. patent application Ser. No. 11/315,992;
"Photosensing Throughout Energy Range and in Subranges", U.S.
patent application Ser. No. 11/316,438; "Position-Based Response to
Light", U.S. patent application Ser. No. 11/633,302; "Photosensing
Optical Cavity Output Light", U.S. patent application Ser. No.
11/702,250; "Encoding Optical Cavity Output Light", U.S. patent
application Ser. No. 11/702,363; "Obtaining Information From
Optical Cavity Output Light", U.S. patent application Ser. No.
11/702,249; "Distinguishing Objects", U.S. patent application Ser.
No. 11/702,328; "Implanting Optical Cavity Structures", U.S. patent
application Ser. No. 11/702,329; "Containing Analyte In Optical
Cavity Structures", U.S. patent application Ser. No. 11/702,325;
and "Tuning Optical Cavities", U.S. patent application Ser. No.
11/702,321.
BACKGROUND OF THE INVENTION
The present invention relates generally to techniques involving
tuning of optical cavities, such as cavities whose output light can
include information.
Various optical cavities have been proposed that have features
related to tuning. U.S. Pat. Nos. 6,295,130 and 6,597,461, for
example, describe two different types of tunable Fabry-Perot
cavities. U.S. Pat. No. 6,285,504 describes a variable optical
filter in which the optical path length of a resonant cavity
between partially reflective surfaces can be varied. U.S. Pat. No.
6,747,775 describes a detunable Fabry-Perot interferometer.
It would be advantageous to have improved techniques for tuning
optical cavities.
SUMMARY OF THE INVENTION
The invention provides various exemplary embodiments, including
products, systems, methods, apparatus, and devices. In general, the
embodiments involve optical cavities that can be tuned to operate
as inhomogeneous optical cavities or to provide laterally varying
intensity distributions.
These and other features and advantages of exemplary embodiments of
the invention are described below with reference to the
accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic diagram of a system in which an optical
cavity device includes a tunable optical cavity that can operate as
an inhomogeneous optical cavity that provides output light with
laterally varying intensity distribution.
FIG. 2 is a schematic side view of a homogeneous optical cavity
that could also be used in a system that includes the optical
cavity device of FIG. 1.
FIG. 3 is a graph showing intensity-energy curves for transmission
and reflection from a cavity as in FIG. 2 when operated as a
Fabry-Perot cavity, showing ways in which information can be
included in transmission mode peaks.
FIG. 4 is a schematic side view of a graded optical cavity that is
an example of an inhomogeneous optical cavity that could be used in
the system of FIG. 1.
FIG. 5 is a graph showing an intensity-position function of a
cavity as in FIG. 4, showing both spectral and harmonic
relationships between peaks.
FIG. 6 is a schematic diagram of a setup in which an optical cavity
as in FIG. 2 or 4 could operate to provide output light with
reflection modes.
FIG. 7 is a schematic diagram of an implementation of the system of
FIG. 1.
FIG. 8 is a schematic circuit diagram of a system implemented as in
FIG. 7.
FIG. 9 is a flow diagram showing operations of the analyte
information routine in FIG. 8.
FIG. 10 is a schematic side view of a device with an optical cavity
that can be tuned by modifying the length of elastomer spacers and
could be used in a system as in FIGS. 7 and 8.
FIG. 11 is a graph showing two transmission spectra that could be
provided by tuning an optical cavity as in FIG. 10.
FIG. 12 is a schematic side view of a graded optical cavity that
can contain analyte and could be used in a system as in FIGS. 7 and
8.
FIG. 13 is a schematic top view of a photosensing component as in
FIG. 12.
FIG. 14 is a flowchart showing operations in producing devices as
in FIGS. 10 and 11.
DETAILED DESCRIPTION
In the following detailed description, numeric values and ranges
are provided for various aspects of the implementations described.
These values and ranges are to be treated as examples only, and are
not intended to limit the scope of the claims. In addition, a
number of materials are identified as suitable for various facets
of the implementations. These materials are to be treated as
exemplary, and are not intended to limit the scope of the
claims.
"Light" refers herein to electromagnetic radiation of any
wavelength or frequency; unless otherwise indicated, a specific
value for light wavelength or frequency is that of light
propagating through vacuum. The term "photon" refers herein to a
quantum of light, and the term "photon energy" refers herein to the
energy of a photon. Light can be described as having a "photon
energy distribution", meaning the combination of photon energies
that are included in the light; highly monochromatic light, for
example, has a photon energy distribution with one peak energy
value. A photon energy distribution can be specified in space and
time: For example, a photon energy distribution can be specified as
a function of position, such as on a surface, or as a function of
time; a photon energy distribution that is "homogeneous" is
substantially the same at all relevant positions, such as the
positions of a surface, while a photon energy distribution that is
"stable" is substantially the same at all relevant times.
Light can also be described as provided by a "light source," which,
unless otherwise specified, refers herein to any device, component,
or structure that can provide light of the type described; examples
of light sources relevant to the below-described implementations
include various kinds of pulsed and unpulsed lasers and laser
structures, light emitting diodes (LEDs), superluminescent LEDs
(SLEDs), resonant cavity LEDs, sources of broadband light that is
spectrally filtered such as with a monochromator, and so forth. A
"tunable light source" is a light source that provides light with a
predominant photon energy that can be changed in response to a
signal or operation of some kind.
The term "laser" is used herein to mean any region, element,
component, or device in which transitions between energy levels can
be stimulated to cause emission of coherent light, such as in the
ultraviolet, visible, or infrared regions of the spectrum. A "laser
structure" is any structure that includes one or more lasers. A
"laser cavity" is a region of a laser in which transitions can be
stimulated to cause emission.
To "propagate" light through a region or structure is to transmit
or otherwise cause the light to propagate through the region or
structure. The light may be referred to as "propagated light" or
"propagating light".
Propagating light can often be usefully characterized by direction
and speed of propagation, with direction typically illustrated by
one or more rays and with speed typically being described relative
to the constant c, also referred to as the speed of light in
vacuum. Where light changes direction in a way that can be
illustrated as a vertex between an incoming ray and an outgoing
ray, the change may be referred to as a "reflection"; similarly, to
"reflect" light is to cause the light to change its direction of
propagation approximately at a surface, referred to herein as a
"reflection surface". Where light propagates at less than c, it may
be useful to obtain an "optical distance" of propagation; for any
segment of length d in which speed of propagation is constant
.epsilon.*c, where .epsilon..ltoreq.1, optical distance
D(.epsilon.)=d/.epsilon.. An optical distance may be referred to
herein as an "optical thickness", such as where light is
propagating through a thickness of material.
"Photon energy information" refers herein to information about
photon energy, such as information about wavelength, frequency,
wavelength shift, frequency shift, or a distribution of wavelengths
or frequencies. "Absolute photon energy information" is information
about a given photon energy value, such as a specific wavelength or
frequency, while "relative photon energy information" is
information that relates two photon energy values, whether measured
concurrently or at different times.
To "photosense" is to sense photons, and to "photosense quantity"
of photons is to obtain information indicating a quantity of the
photons. Photons that are photosensed are sometimes referred to
herein as "incident photons". A surface at which photosensing
occurs is referred to herein as a "photosensitive surface".
A "photosensor" is used herein to refer generally to any element or
combination of elements that senses photons, whether by
photosensing quantity or any other information about the photons. A
photosensor could, for example, provide an electrical signal or
other signal that indicates results of sensing, such as a signal
indicating quantity of incident photons; in general, signals from a
photosensor that indicate results of sensing are referred to herein
as "sensing results". If electrical sensing events occur in a
photosensor in response to incident photons, the photosensor may
integrate or otherwise accumulate the results of the electrical
sensing events during a time period referred to herein as a
"sensing period" or "sense period".
A "range of photon energies" or an "energy range" is a range of
energy values that photons can have. An energy range can be
described, for example, as a range of wavelengths or a range of
frequencies or, in appropriate cases, by the range's central
wavelength or frequency and possibly also the range's width. A
"subrange" of a range of photon energies is a part of the range,
and can be similarly described. A central wavelength or frequency
or other value indicating a central photon energy of a range or
subrange is sometimes referred to herein as a "central energy", and
may be obtained in various ways, such as by finding an energy that
has maximum intensity or that is another type of central value such
as a mean or median of the distribution of light within the range
or subrange.
In general, the upper and lower boundaries and widths of ranges and
subranges are approximate. To provide output photons or to
photosense quantity of photons "throughout", "within", or "in" a
range or subrange means to provide photons or to obtain information
about quantity of photons that are predominantly within the range
or subrange. In typical cases, between 60-90% of the provided
photons or sensed quantity of photons have energies within the
range or subrange, but the percentage could be lower or higher. In
some applications, 90% or even 95% or more of the provided photons
or sensed quantity of photons have energies within the range or
subrange.
Some of the photosensing implementations described herein employ
structures with one or more dimensions smaller than 1 mm, and
various techniques have been proposed for producing such
structures. In particular, some techniques for producing such
structures are referred to as "microfabrication." Examples of
microfabrication include various techniques for depositing
materials such as growth of epitaxial material, sputter deposition,
evaporation techniques, plating techniques, spin coating, printing,
and other such techniques; techniques for patterning materials,
such as etching or otherwise removing exposed regions of thin films
through a photolithographically patterned resist layer or other
patterned layer; techniques for polishing, planarizing, or
otherwise modifying exposed surfaces of materials; and so
forth.
In general, the structures, elements, and components described
herein are supported on a "support structure" or "support surface",
which terms are used herein to mean a structure or a structure's
surface that can support other structures. More specifically, a
support structure could be a "substrate", used herein to mean a
support structure on a surface of which other structures can be
formed or attached by microfabrication or similar processes.
The surface of a substrate or other support surface is treated
herein as providing a directional orientation as follows: A
direction away from the surface is "up", "over", or "above", while
a direction toward the surface is "down", "under", or "below". The
terms "upper" and "top" are typically applied to structures,
components, or surfaces disposed away from the surface, while
"lower" or "underlying" are applied to structures, components, or
surfaces disposed toward the surface. In general, it should be
understood that the above directional orientation is arbitrary and
only for ease of description, and that a support structure or
substrate may have any appropriate orientation.
Unless the context indicates otherwise, the terms "circuitry" and
"circuit" are used herein to refer to structures in which one or
more electronic components have sufficient electrical connections
to operate together or in a related manner. In some instances, an
item of circuitry can include more than one circuit. An item of
circuitry that includes a "processor" may sometimes be analyzed
into "hardware" and "software" components; in this context,
"software" refers to stored or transmitted data that controls
operation of the processor or that is accessed by the processor
while operating, and "hardware" refers to components that store,
transmit, and operate on the data. The distinction between
"software" and "hardware" is not always clear-cut, however, because
some components share characteristics of both; also, a given
software component can often be replaced by an equivalent hardware
component without significantly changing operation of
circuitry.
Circuitry can be described based on its operation or other
characteristics. For example, circuitry that performs control
operations is sometimes referred to herein as "control circuitry"
and circuitry that performs processing operations is sometimes
referred to herein as "processing circuitry".
An "integrated circuit" or "IC" is a structure with electrical
components and connections produced by microfabrication or similar
processes. An IC may, for example, be on or over a substrate on
which it was produced or another suitable support structure. Other
components could be on the same support structure with an IC, such
as discrete components produced by other types of processes.
Implementations of ICs and photosensing components described herein
include features characterized as "cells" (or "elements") and
"arrays", terms that are used with related meanings: An "array" is
an arrangement of "cells" or "elements"; unless otherwise indicated
by the context, such as for a biological cell, the words "cell" and
"element" are used interchangeably herein to mean a cell or an
element of an array. An array may also include circuitry that
connects to electrical components within the cells such as to
select cells or transfer signals to or from cells, and such
circuitry is sometimes referred to herein as "array circuitry". In
contrast, the term "peripheral circuitry" is used herein to refer
to circuitry on the same support surface as an array and connected
to its array circuitry but outside the array. The term "external
circuitry" is more general, including not only peripheral circuitry
but also any other circuitry that is outside a given cell or
array.
Some of the implementations below are described in terms of "rows"
and "columns", but these terms are interchangeable. Also, rows and
columns are described herein as examples of "lines". Within an
array, a "line" of cells refers herein to a series of cells through
which a line can be drawn without crossing areas of cells that are
not in the line. For example, in a two-dimensional array in which
cells have uniform areas, a line of cells could be a row, a column,
a diagonal, or another type of straight line; more generally, a
line of cells could be straight or could include one or more
non-straight features, such as curves or angles.
An IC includes a "photosensor array" if the IC includes an array of
cells, and at least some of the cells include respective
photosensors. A cell that includes a photosensor may also include
"cell circuitry", such as circuitry that makes connections with the
photosensor, that transfers signals to or from the photosensor, or
that performs any other operation other than photosensing. In
general, a cell's photosensor and cell circuitry are within a
bounded area of the array, an area sometimes referred to herein as
the "cell's area". The part of a cell's area in which an incident
photon can be photosensed is referred to herein as "sensing
area".
In an application of an IC that includes a photosensor array,
circuitry that "responds to" one or more photosensors can be any
circuitry that, in operation, receives information from the
photosensors about their photosensing results through an electrical
connection. Circuitry that responds to a photosensor could be
circuitry in the same cell as the photosensor, or it could be array
circuitry, peripheral circuitry, or other external circuitry, or it
could include any suitable combination of cell circuitry, array
circuitry, peripheral circuitry, and other external circuitry.
Circuitry that responds to a photosensor could employ any suitable
technique to read out photosensing results, including, for example,
CCD, CMOS, or photodetector array (PDA) techniques.
An IC is or includes a "position-sensitive detector" or "PSD" if it
includes a substantially continuous photosensitive surface and it
provides electrical signals indicating a position resulting from a
pattern of incident light on the photosensitive surface. For
example, the signals could be two currents whose normalized
difference is proportional to a centroid of the incident light
pattern.
FIG. 1 illustrates general features of system 10, an example of a
system that can be implemented as described in greater detail
below. As with other implementations described below, system 10
involves a combination of parts or components. As used herein, a
"system" is a combination of two or more parts or components that
can perform an operation together. A system may be characterized by
its operation: for example, an "analyte information system" is a
system that operates somehow on analyte information; a "processing
system" is a system that performs data or signal processing; and so
forth.
Within a system, components and parts may be referred to in a
similar manner. One component of an analyte information system in
which information is obtained about an analyte's optical
characteristics, for example, can be a "detector component" or
simply "detector", meaning a component that detects light;
similarly, a "light source component" includes one or more light
sources; an "optical component" performs an optical operation; a
"photosensing component" performs a photosensing operation; a
"deformable component" that can be changed in shape in response to
stress or other internal or external forces, some examples of which
are described below; a "signal-responsive component"; an "electrode
component" or simply "electrode", meaning an electrically
conductive part that is connected to a current path and is of the
sort that operates in relation to one or more other electrode, such
as by controlling an electrostatic field between the electrodes or
by establishing electrical contact to a component that is between
electrodes in a circuit; a "sensing component" that can sense an
item, e.g. a shape of a deformable component; a "light-transmissive
component" or simply "transmission component" transmits light; a
"light-reflective component" or simply "reflective component"
reflects light; and other examples are defined further below. Other
parts or components can be characterized by their structure.
In the implementations described below, structures, systems, or
parts or components of structures or systems may sometimes be
referred to as "attached" to each other or to other structures,
systems, parts, or components or visa versa, and operations are
performed that "attach" structures, systems, or parts or components
of structures or systems to each other or to other things or visa
versa; the terms "attached", "attach", and related terms refer to
any type of connecting that could be performed in the context. One
type of attaching is "mounting", which occurs when a first part or
component is attached to a second part or component that functions
as a support for the first. In contrast, the more generic term
"connecting" includes not only "attaching" and "mounting", but also
making other types of connections such as electrical connections
between or among devices or components of circuitry. A combination
of one or more parts connected in any way is sometimes referred to
herein as a "structure".
A structure may be described by its operation, such as a "support
structure" that can operate as a support as described above;
similarly, an "optical cavity structure" includes parts or
components that can operate as an optical cavity; a "tuning
structure" that can perform a tuning operation; other examples are
defined below. In addition, a structure may be characterized by the
nature of its parts or the way in which they are connected; for
example, a "layered structure" is a structure that includes one or
more layers, and a "partial structure" refers to a structure that
is in turn part of another structure.
System 10 includes device 12, control circuitry 14, and
photosensitive component 16. Device 12 in turn includes
light-reflective components 20 and 22 and, between them,
light-transmissive region 24 into which components 20 and 22
reflect light, so that light-transmissive region is between two
inward reflection surfaces provided by components 20 and 22. Device
12 also includes tuning structure 30, a structure than can respond
to tuning signals, illustratively from control circuitry 14, by
moving light-reflective components 20 and 22 relative to each
other, which has the effect of tuning optical cavity operation by
moving its inward reflection surfaces relative to each other. As
used herein, an optical cavity's operation, or the optical cavity
itself, is "tuned" when it is changed in some way, such as by
changing the shape of its light-transmissive region so that it
transmits a different wavelength range; as used herein, an optical
cavity's "shape" refers to the shape of its light-transmissive
region.
Tuning structure 30 illustratively includes one or more deformable
components 32 and one or more signal-responsive components 34,
although tuning could be performed in many other ways, with or
without deformable components. Deformable components 32 could
optionally each be an "elastically deformable component", meaning a
deformable component of any kind that can return at least
approximately to a previous shape after deformation; as used
herein, elastically deformable components could be, but need not
be, spring-like, and an elastically deformable component could
require at least some force to return it to its previous shape,
which would also be treated as a deformation; but in some
implementations with only a single adjustment, elasticity would not
be required. Also, the term "shape" is used herein to encompass
size, so that a deformable component (whether or not elastic), in
addition to being deformed by forces that change the category or
proportions of its shape, is also considered deformed by a force
that changes only its size; therefore, a deforming force could
allow a deformable component to retain a shape of the same
category, such as a cylinder or cube, with all its dimensions
similarly scaled as it changes size, as can occur, for example,
with some inflatable components.
Signal-responsive components 34 receive tuning signals, and, in
response, cause deformation of deformable components 32, such as
electrostatically, electromagnetically, magnetically,
piezoelectrically, thermally, or mechanically. Deformable
components 32 are connected so that deformation caused by
signal-responsive components 34 in turn causes light-reflective
components 20 and 22 to move relative to each other, changing the
optical cavity's shape; for example, either of light-reflective
components 20 and 22 could move while the other remains at a fixed
position or both could move, such as relative to a support
structure. Deformable components 32 can be at least partially
within light-transmissive region 24 as shown or can have surface
area that bounds or extends into light-transmissive region 24, but
within light-transmissive region 24 there could also be an analyte
region in which analyte can be present, such as an opening defined
in and bounded by deformable components 32 (and there could also be
a reference region containing a reference fluid or the like).
Presence of analyte in region 30 affects the cavity's output light
when the cavity's operation is tuned to certain relative positions
of the inward reflection surfaces, referred to as a "set of
relative positions". A set of relative positions can include a
"range of relative positions", referring to a substantially
continuous subset of the set. The inward reflection surfaces can
take a "sequence of relative positions" that occur in an order in
time, and an optical cavity can similarly have a "sequence of . . .
shapes".
Bidirectional arrows 36 illustrate a range of positions through
which light-reflective component 20 can move relative to
light-reflective component 22 in response to deformation of
components 32, with another position of light-reflective component
20 being illustrated by dashed outline 38. Therefore, operation of
signal-responsive components 34 causes light-reflective components
20 and 22 to move relative to each other within the range of
positions indicated by arrows 36. The range includes a subrange of
one or more positions in which components 20 and 22 and
light-transmissive region 24, possibly with analyte in the light
transmissive region, can operate as an optical cavity that provides
output light. If analyte is present, the output light can include
information about optical characteristics of the analyte.
The term "reflective optical cavity", or simply "optical cavity" or
"cavity", refers herein to a light-transmissive region that is at
least partially bounded by light-reflective components, with the
light-reflective components and the light-transmissive region
having characteristics such that a measurable portion of light
within the light-transmissive region is reflected more than once
across the light-transmissive region. An "optical cavity component"
or "optical cavity device" is a component or device, respectively,
that includes one or more optical cavities.
Within the broad category of optical cavities, there are various
more specific types: For example, a laser cavity, mentioned above,
is an example of an "emitting optical cavity" or simply "emitting
cavity" that can operate as a source of emitted output light even
when it is not receiving input light from an external light source,
with the emitted light ordinarily resulting from a gain medium
within the light-transmissive region; similarly, a "transmissive
cavity" can operate, in response to input light from one or more
external light sources at an entry surface, providing a transmitted
portion of its output light at an exit surface different than the
entry surface (a complementary, reflected portion may be provided
at the entry surface); a "Fabry-Perot cavity" is a reflective
optical cavity in which constructive interference (or positive
reinforcement) occurs in one or more photon energy subranges while
destructive interference occurs in others.
A Fabry-Perot cavity or other optical cavity that can operate to
provide output light in one or more photon energy subranges while
not providing output light with other photon energies may be
described as having one or more "modes", each for a respective one
of the output light energy subranges; if the cavity is a
transmissive cavity, modes of its transmitted output light may be
referred to as "transmission modes" and modes of its reflected
output light may be referred to as "reflection modes". In the
reflection spectrum, either the valley-like dips or the
plateau-like reflection bands between the dips can be considered a
"reflection modes". An emitting cavity can be described as
"stimulated at" a mode by any operation that results in emission of
output light in the mode's photon energy subrange. Similarly, a
transmissive cavity can be described as "illuminated at" a mode by
any operation that provides input light that results in
transmission or reflection of output light in the mode's photon
energy subrange.
In typical implementations of optical cavities, two
light-reflective components have approximately parallel reflection
surfaces and the light-transmissive region is sufficiently uniform
that measurements would indicate many reflections of light within
the light-transmissive region. Such cavities define a directional
orientation as follows: Directions in which light could propagate
and be reflected many times within the light-transmissive region
are referred to herein as "reflection directions", and generally
include a range of directions that are approximately perpendicular
to both reflection surfaces. Directions that are approximately
parallel to both reflection surfaces, on the other hand, are
generally referred to herein as "lateral directions". In addition,
the terms "in", "inward", or "internal" generally refer to
positions, directions, and other items within or toward the
light-transmissive region between the reflection surfaces, while
"out", "outward", and "external" refer to positions, directions,
and other items outside or away from the light-transmissive region.
In general, it should be understood that the above directional
orientation is arbitrary and only for ease of description, and that
an optical cavity may have any appropriate orientation.
The above directional orientation does not in general apply to
angle of incidence of input light. Transmissive cavities can
typically operate in response to incident light that is not
perpendicular to entry surfaces or reflection surfaces. Light
incident on a transmissive cavity's entry surface at any angle is
reflected multiple times within the cavity, producing transmission
modes in accordance with the cavity's geometry. But transmission
modes are affected by angle of incidence: Depending on the type of
cavity and the angle of incidence, modes can be blue shifted or red
shifted in comparison to perpendicular incidence; if all light
enters a cavity at approximately the same angle, performance is
affected only by the shifting of modes and modes are not also
broadened, but performance is reduced if a cavity receives incident
light distributed across a large angular range because transmission
mode structure is then averaged over multiple angles.
Analyte is "present in", "positioned in", "contained in", or simply
"in" an optical cavity when the analyte is in all or some part of
the cavity's light-transmissive region; the optical cavity may be
said to "contain" the analyte or to be an "analyte-containing
optical cavity". An optical cavity provides "analyte-affected
output light" if the optical cavity's output light is different in
some way when analyte is present in the cavity than when analyte is
absent, with the difference being due to the analyte's optical
characteristics.
More generally, a cavity "includes a region" if the region is all
or some part of the cavity's light-transmissive region. An "analyte
region", therefore, is a region that can contain analyte.
The various exemplary implementations described below address
problems that arise in operating tunable optical cavities, such as
transmissive Fabry-Perot cavities. The implementations are
especially relevant to output light that includes information about
an analyte's optical characteristics, but the general cavity tuning
techniques described herein address problems that relate to a
multitude of other uses of tunable optical cavities, including
various uses of inhomogeneous optical cavities, like linear
variable filters (LVFs). One problem is that previous techniques
provide limited flexibility in how an optical cavity could be
tuned, in part because certain cavity features are typically fixed
or inflexible. Another is that some techniques rely on complex and
expensive ways to manufacture, use, or tune cavities. In
particular, previous techniques do not provide sufficiently
adjustable thickness and tilt of an inhomogeneous optical cavity,
such as one containing an analyte, to enable optimized performance
in a certain wavelength range and/or in a particular application;
such techniques are also inflexible in not allowing both for
adjustment during fabrication of an inhomogeneous cavity and also,
with substantially the same mechanism, allowing adjustment of the
cavity before and during a sequence of measurements, such as where
measurements are being made at different wavelengths.
As shown in FIG. 1, the illustrated optical cavity is illuminated
by input light, represented by arrows 40, received through
light-reflective component 20. In response, the optical cavity
operates to provide output light. As illustrated, however,
light-reflective components 20 and 22 are not parallel, which
represents graphically a feature of the optical cavity: It has
"laterally varying optical distance" or "laterally varying optical
thickness" between reflective surfaces provided by components 20
and 22, meaning that the optical distance between the reflective
surfaces varies in one or more lateral directions. Optical cavities
with laterally varying optical distance could be produced in many
ways, several of which are described in co-pending U.S. patent
application Ser. No. 11/316,438, entitled "Photosensing Throughout
Energy Range and in Subranges" and incorporated herein by reference
in its entirety.
As a consequence of laterally varying optical distance, the optical
cavity also has a "laterally varying energy output function",
meaning that photon energies of its output light depend on lateral
position, and is therefore an example of an "inhomogeneous" optical
cavity, which simply means that it is not a "homogeneous optical
cavity", used herein to refer to an optical cavity whose
light-transmissive region includes an extended part with
substantially constant optical distance D between its reflection
surfaces, sometimes referred to as its "homogeneous region".
In FIG. 1, the laterally varying energy output function can be
modified or "tuned" by changing the relative positions of
components 20 and 22 in an appropriate sequence, producing a
sequence of optical cavity shapes. As shown, the reflection
surfaces provided by components 20 and 22 can each lie
approximately in a plane, in which case tuning can be done by
changing the angle at which the planes would meet if projected,
also called the "tilt angle". As can be seen, as component 20
changes from its initial position to the position indicated by
outline 38, the tilt angle increases, resulting in a corresponding
increase in the range of optical distance between the cavity's
reflection surfaces and therefore greater lateral variation in the
energy output function. On the other hand, tilt angle decrease
results in reduced lateral variation, with the optical cavity being
substantially homogeneous at a tilt angle of zero if the reflection
surfaces are parallel and the light-transmissive region between
them is homogeneous.
A tunable inhomogeneous optical cavity as in FIG. 1 can also be
tuned without changing the tilt angle, simply by increasing or
decreasing distance between reflection surfaces. This tuning
mechanism changes the optical distance at each lateral position,
thereby changing the shape and the laterally varying energy output
function. In addition, if the distance between reflection surfaces
is changed by an equal amount at each lateral position, the effect
will be proportionally larger where the optical distance is smaller
and vice versa.
It is also possible to tune an inhomogeneous optical cavity by
concurrently changing both tilt angle and also distance between
reflection surfaces, and both kinds of tuning could be performed in
more complex ways than shown in FIG. 1. Other tuning techniques
could also be used, such as changing the contents of the
light-transmissive region. Furthermore, if an inhomogeneous optical
cavity can be precisely tuned, it becomes possible to select its
range of transmitted photon energies with precision: One could
select a range that includes exactly one or some other number of
transmissive or reflective modes or a range that includes a
specific desired wavelength. By modulating the tuning operation, it
also becomes possible to use lock-in techniques to increase
sensitivity with which position on a photosensitive surface (which
can indicate wavelength) is photosensed.
In FIG. 1, the optical cavity is operated to provide output light
with a "laterally varying intensity distribution", meaning an
intensity distribution that varies in one or more lateral
directions. This can occur as a result of the lateral variation in
energy output function in accordance with the optical cavity's
shape: For example, if the input light is uniformly distributed in
lateral directions, but has an intensity peak within a narrow band
of wavelengths, the optical cavity transmits the input light only
in certain regions in which it has a transmission mode that
overlaps with the narrow band of wavelengths. Therefore, the output
light will have greater intensity in those regions and lower
intensity in other regions in which it does not have a transmission
mode that overlaps the narrow band. A laterally varying intensity
distribution of this type is also a "laterally varying photon
energy distributions" or simply "laterally varying energy
distributions", meaning a distribution in which photon energy of
light varies as a function of lateral position.
Photosensing component 16 receives the output light on
photosensitive surface 42, and the graph shown in the boundary of
photosensitive surface 42 illustrates features of the laterally
varying intensity distribution; The graph shows an "intensity
function" for each of two relative positions of components 20 and
22, meaning that the graph represents intensity of output light
from each of the relative positions as a function of another
parameter, such as of photon energy or, in some implementations, of
position. In this case, the two intensity functions are
"intensity-position functions", showing intensity as a function of
position on photosensitive surface 42.
An intensity function can have any of a wide variety of shapes and
features, but a shape that frequently arises in transmission modes
is the "peak", a shape characterized by a maximum value from which
a curve for the function slopes steeply downward. Peaks have
various features, including "central value", meaning the value of
the other parameter at which the peak's maximum occurs, such as
"central energy" for an intensity-energy function; "maximum
intensity" or simply "maximum" or "amplitude", meaning the
intensity value at the peak's maximum, whether measured as an
absolute intensity or relative to another feature, such as a nearby
minimum value; "contrast", meaning a value indicating relationship
between magnitudes of the peak's maximum intensity and of one or
more nearby minima of the transmission intensity function; and
"intermediate intensity width", meaning the width of the peak at an
intensity somewhere between its maximum and nearby minima, such as
a full width half maximum (FWHM). In general, information can be
encoded in one of these features in various ways, including those
described in co-pending U.S. patent application Ser. No.
11/702,363; entitled "Encoding Optical Cavity Output Light" and
incorporated herein by reference in its entirety. Once encoded,
such information can also be recovered in various ways, including
those described in co-pending U.S. patent application Ser. No.
11/702,249; entitled "Obtaining Information From Optical Cavity
Output Light" and incorporated herein by reference in its
entirety.
The graph in FIG. 1 shows two intensity peaks: Intensity peak 44,
in solid line, results from the initial relative position of
components 20 and 22 in which there are a smaller tilt angle and
smaller optical distances between the components; intensity peak
46, in dashed line, results from the position represented by
outline 38, in which both tilt angle and optical distances are
larger. As a result of these changes, the central value of
intensity peak 46 has shifted in position and the FWHM (or other
intermediate intensity width) of the peak is getting smaller as a
consequence of the larger tilt. In each position, photosensing
component 16 can provide sensing results with information from the
intensity distribution incident on photosensitive surface 42. In
addition, in some implementations, photosensing component 16 can
provide sensing results with information about the change or
"shift" of position from peak 44 to peak 46 as well as the change
of the FWHM. Techniques for measuring positions and shifts of
position are described in greater detail in co-pending U.S. patent
application Ser. No. 11/633,302, entitled "Position-based Response
to Light" and incorporated herein by reference in its entirety.
Also, techniques for encoding information about analytes in
intensity peaks are described in co-pending U.S. patent application
Ser. No. 11/702,363; entitled "Encoding Optical Cavity Output
Light" and incorporated herein by reference in its entirety.
The general features in FIG. 1 could be implemented in many ways,
as exemplified by the various implementations described below. In
particular, the exemplary implementations below include examples of
how control circuitry could control tuning structures by providing
signals to signal-responsive components, and many other types of
control circuitry, signal-responsive components, and control
techniques could be employed. Control circuitry 14 could be
implemented, for example, to tune the optical cavity during
fabrication, during use, or both, and can therefore be used to tune
the optical cavity for a specific application, such as a sensing
application in which it functions as an LVF with a particular
gradient. For example, a coarse tuning operation could be performed
during fabrication, and a fine tuning operation during use, with
fine tuning possibly being performed in order to obtain information
about an analyte within the optical cavity as described in
co-pending U.S. patent application Ser. No. 11/702,321; entitled
"Tuning Optical Cavities" and incorporated by reference herein in
its entirety.
Many different types of mirrors and other light-reflective
components could be used in an optical cavity device, some of which
are described below. Also, elastomer spacers and various other
kinds of deformable components could be used in optical cavity
tuning, some examples of which are described below. Further,
spacers or other deformable components could be connected to cause
mirror movement in any of a wide variety of ways. For example, they
could be connected as a result of a fabrication technique in which
spacers are formed as by photolithography on the mirrors.
Furthermore, various bonding, adhesive, or similar techniques could
be used to make a similar connection between them.
Photosensing component 14 could be implemented in many different
ways, such as with a photosensing IC, as described in co-pending
U.S. patent application Ser. No. 11/702,250; entitled "Photosensing
Optical Cavity Output Light" and incorporated by reference herein
in its entirety. In particular, photosensitive surface 42 could
have characteristics such that it can serve as a support surface or
substrate for fabrication of optical cavity device 12, such as with
thin film techniques which allow flexible and cheap fabrication
using dielectric and metal mirrors on a photosensitive surface or
any other suitable surface. Alternatively, some or all of the
components of optical cavity device 12 could instead be attached or
otherwise connected on or over photosensitive surface 42, possibly
with one or more optical components between, though it is
advantageous in many implementations to have the shortest possible
optical path from the optical cavity to a photosensitive surface,
such as to optimize signal-to-noise ratio. The main task of
photosensing component 16 is to measure the spatial intensity
distribution at the exit mirror of the inhomogeneous cavity. In an
especially elegant implementation, this can be done by directly
attaching the cavity's exit surface to photosensing component 16;
another possible approach is to image the output light onto
photosensing component 16 with one or more optical components.
FIG. 2 illustrates optical cavity 100, an example of a homogeneous
optical cavity. The homogeneous region of cavity 100 illustratively
includes substantially all of light-transmissive region 102 where
it is between and partially bounded by light-reflective components
104 and 106, though partially and completely bounded homogeneous
regions with various other shapes and arrangements are
possible.
Inward-facing surfaces 110 and 112 of components 104 and 106,
respectively, can be implemented, for example, as mirrors or other
reflective components that closely approximate the reflection
surfaces of cavity 100. The characteristics of components 104 and
106 and of any material or structure within region 102 are such
that a measurement would indicate that at least a portion of light
within region 102 is reflected more than once. A reflection
direction in which light can be repeatedly reflected between the
reflection surfaces is represented by bidirectional ray 114, while
one of the possible lateral directions in an x-y plane
approximately perpendicular to ray 114 is illustrated by an x-axis
at the lower right.
FIG. 2 also illustrates two ways in which homogeneous optical
cavities can operate to provide output light, represented
schematically by arrows 116. In both operations, output light can
be provided at an exit surface, illustratively outward-facing
surface 120 of component 106, which may or may not be approximately
parallel to the reflection surfaces.
In the first operation, optical cavity 100 operates as an emitting
cavity, such as a laser cavity. Typically, an emitting cavity
operates in response to stimulation of some type, represented
schematically in FIG. 2 by stimulation arrow 122. Stimulation arrow
122 could, for example, represent electrical or optical
stimulation.
In the second operation, optical cavity 100 operates as a
transmissive cavity, such as a Fabry-Perot interferometer. A
transmissive cavity operates in response to input light from one or
more external light sources, represented in FIG. 2 by illumination
arrows 124. Input light can be received at an entry surface,
illustratively outward-facing surface 126 of component 104, which
also may or may not be approximately parallel to the reflection
surfaces. As noted above, a reflected portion of output light can
be provided at the entry surface, as described in greater detail
below.
FIG. 3 is an intensity-energy graph or "output spectrum" for
optical cavity 100 when operated as a Fabry-Perot cavity such as an
interferometer. Since photon energy is inversely proportional to
wavelength, wavelength increases as one moves leftward along the
horizontal axis, while the inverse of the wavelength (1/.lamda.)
increases as one moves rightward, as suggested by the labeling of
points on the horizontal axis; it follows that energy and frequency
would also increase to the right.
The graph in FIG. 3 includes a solid-line curve with peaks 130,
132, and 134, each of which is an "intensity-energy peak" or simply
"intensity peak" that results from a respective transmission mode
of cavity 100, illustratively the Kth, (K-1)th, and (K-2)th modes,
and has an amplitude Imax, which could result from broadband
illumination in the photon energy subranges of all the modes shown;
such a curve is sometimes referred to herein as a "transmission
spectrum". FIG. 3 also includes part of dashed-line curve 136 that
is the complement of the transmission spectrum, i.e. the
intensity-energy curve for light that is reflected rather than
transmitted by optical cavity 100; such a curve is sometimes
referred to herein as a "reflection spectrum" and its reflection
modes are broad and separated by narrow valleys rather than being
narrow peaks separated by broad valleys like the transmission
modes. The term "output modes" is sometimes used herein as a
generic term that encompasses transmission modes and reflection
modes.
The maxima of intensity-energy peaks 130, 132, and 134 (and the
complementary minima between reflection bands) are spaced apart as
a function of photon energy (illustratively wavelength), and the
difference between the central energy of adjacent transmission mode
peaks is referred to as "free spectral range" or "FSR". FSR can be
treated as the bandwidth over which adjacent intensity-energy peaks
do not overlap, while the full width half maximum (FWHM) of the
peaks can be treated as the minimum resolvable bandwidth. FSR,
FWHM, and their ratio are all sometimes treated as figures of merit
in designing a Fabry-Perot cavity.
The wavelength .lamda. of each intensity-energy peak can be
obtained from the equation .lamda.(k)=2nD/k, where n is the
refractive index of the cavity and k is a non-zero integer.
Therefore, if refractive index of the cavity changes, .lamda.(k)
also changes for a given value of k, so that if a peak's central
energy changes, as indicated by .DELTA..lamda.+ and .DELTA..lamda.-
for peak 134, the change provides information about refractive
index change. Similarly, the intensity of the peaks depends on
absorption in the cavity, so that if the intensity of a peak
departs from Imax, as indicated by .DELTA.I+ and .DELTA.I- for peak
134, the change provides information about absorption change.
FIG. 4 illustrates graded optical cavity 150, an example of an
inhomogeneous optical cavity. Because of the similarities between
cavities 150 and 100, parts and components of cavity 150 that are
substantially the same as those in FIG. 2 are labeled with the same
reference numbers. In cavity 150, however, region 152 is not
homogeneous, but rather has laterally varying optical distance
between reflective surfaces, as described above; in the illustrated
example, the optical distance illustratively increases linearly
from D(0) at one end of cavity 150 (x=0) to D(Xmax) at the opposite
end (x=Xmax), but optical distance between reflective surfaces in
an inhomogeneous optical cavity could vary laterally in any
appropriate way, and need not vary monotonically, linearly, or with
any other type of uniformity.
Because of its linearly varying optical distance or thickness,
cavity 150 can operate as a linearly variable optical filter or
linear variable filter (LVF), a type of transmissive cavity. This
capability is illustrated by the function T(x), a laterally varying
energy output function as described above; in this case, the
function relates output photon energy (in response to input light
represented by illumination arrows 124) to lateral position on exit
surface 120. For an LVF, the simple relationship
.lamda.(x)=T(x)=d'x+.lamda.(0) can hold, where d' is a constant
that depends on gradient of optical thickness and can be
graphically represented by the constant slope
(.lamda.(X2)-.lamda.(X1))/(X2-X1)) of position-wavelength graph 154
at right in FIG. 4.
In general, the characteristics of output light at each position on
surface 120 can be a function of parameters other than optical
thickness, including, for example, photon energy and incident
direction of input light 124 received at counterpart positions on
surface 126. In particular, the output light may depend on whether
the input light is narrow band, broad band, or multi-modal, as can
result from a set of transmission or reflection modes. Narrow band
or multi-modal illumination of an LVF, for example, can produce one
or several output light spots, respectively.
The graphs at right in FIG. 4 also illustrate intensity-energy
peaks 160 and 162 that would result if cavity 150 were illuminated
by narrow band input light with central energy of .lamda.(X1) and
.lamda.(X2), respectively, and, in response, operated as an LVF as
described above. At position X1, for example, T(X1) results in
transmission of output light represented by arrow 164, within a
photon energy subrange characterized by central energy .lamda.(X1);
at position X2, T(X2) results in transmission of output light
represented by arrow 166, within a photon energy subrange
characterized by central energy .lamda.(X2); for the illustrated
laterally varying energy output function, if X1.noteq.X2 and the
difference between X2 and X1 is sufficient, then T(X1).noteq.T(X2),
and .lamda.(X1).noteq..lamda.(X2). On the other hand, for
relatively small regions of output surface 120, cavity 150 might in
some cases operate locally as a homogeneous cavity with
transmission modes as illustrated in FIG. 3. It follows that
parameters applicable to transmission modes are sometimes also
useful for intensity-energy peaks from inhomogeneous cavities; in
particular, information about changes in refractive index and
absorption can sometimes be provided through changes in
intensity-energy peaks in ways shown in FIG. 3. Often, however,
output light from an inhomogeneous cavity is more easily
represented with an intensity-position graph, an example of which
is described below.
Various techniques can be used to operate optical cavities to
produce laterally varying photon energy distributions. Such
distributions can be produced, for example, with inhomogeneous
optical cavities having laterally varying optical thicknesses and,
even with homogeneous optical cavities, with angled illumination
from a point light source rather than perpendicular illumination;
several possible techniques are described in co-pending U.S. patent
application Ser. No. 11/316,438, entitled "Photosensing Throughout
Energy Range and in Subranges" and incorporated herein by reference
in its entirety.
More generally, an inhomogeneous optical cavity can have any
appropriate laterally varying energy output function, including
functions that are nonlinear or nonuniform in other ways. Some of
the below-described implementations, for example, involve functions
that are affected by presence of an analyte in an optical cavity.
As with homogeneous cavities, an inhomogeneous cavity's
light-transmissive region can be completely between and partially
bounded by light-reflective components as in FIG. 4, but partially
and completely bounded light-transmissive regions with various
other shapes and arrangements are possible.
FIG. 5 is an intensity-position graph for optical cavity 150 when
operated as a Fabry-Perot cavity such as an interferometer. FIG. 5
is similar to FIG. 3, and the peaks illustratively have maximum
amplitude Imax as in FIG. 3 and their central energies and
amplitudes (and FWHMs) could be affected as shown for peak 134 in
FIG. 3, and their contrasts could also be affected; but the x-axis
in FIG. 5 represents position in the x-direction in FIG. 4 rather
than photon energy.
In the example shown in FIG. 5, cavity 150 is illuminated at P
(P.gtoreq.2) photon energies ranging from .dbd.min to .lamda.max,
resulting in a series of output modes (illustratively transmission
modes) for each photon energy .lamda.(p) of illumination at those
positions on the x-axis where the condition .lamda.(p)=2n*D(x)/k is
satisfied for integer values of k. The first transmission mode
shown for .lamda.min is peak 170 at x=Xmin(1) and for .lamda.max is
peak 172 at x=Xmax(1). The second transmission mode shown for
.lamda.min is peak 174 at x=Xmin(2) and for .lamda.max is peak 176
at x=Xmax(2). The third transmission mode shown for .lamda.min is
peak 178 at x=Xmin(3), and so forth.
In the example of FIG. 5, transmission modes are sufficiently
separated along the x-axis to prevent interference between adjacent
transmission modes. As can be seen, Xmin(2) is sufficiently greater
than Xmax(1) that peaks 172 and 174 do not interfere, and Xmin(3)
is similarly sufficiently greater than Xmax(2) that peaks 176 and
178 do not interfere. If instead the first transmission mode of
.lamda.max were peak 180 due to an increase from Xmax(1) to
Xmax(error), as indicated by arrow 182, interference between peaks
180 and 174 would begin to occur; as the first transmission mode of
.lamda.max increased further, loss of information would occur due
to ambiguity between peak 180 and peak 174. Problems of this type
can be avoided by coordination of photon energy range with cavity
parameters; for example, cavity thickness D can be sufficiently
small that only one output mode occurs over the range from
.lamda.min to .lamda.max. The free spatial range (FSR) between the
modes in a particular wavelength range can also be increased by
reducing the tilt of the inhomogeneous (graded) cavity.
FIG. 6 shows a setup in which optical cavity structure 190 receives
input light represented by arrows 192 through beam splitter 194.
Optical cavity structure 190 can include a transmissive cavity
implemented as in any of the ways described in relation to FIGS.
2-5 or in any other suitable way. In response to the input light,
the cavity provides a transmitted portion of output light
represented by arrows 196 and a reflected portion of output light
represented by arrows 198. The use of beam splitter 194 is merely
illustrative of ways in which input light and reflected light could
be separated; for example, input light could be incident upon an
entry surface at a sufficiently large angle from the normal that
reflected light is separated from input light, though the
non-perpendicular angle of incidence reduces performance of the
optical cavity.
As suggested above in relation to FIG. 3, refractive index changes
in the optical cavity will cause the same shift in both transmitted
and reflected modes, while absorption in the optical cavity will
similarly cause decreased amplitude and contrast and increased FWHM
in both portions, with the effect of absorption typically varying
as a function of photon energy; a curve showing absorption as a
function of photon energy is sometimes referred to herein as an
"absorption spectrum".
FIG. 7 shows system 200, an exemplary implementation of system 100
in FIG. 1. System 200 includes optical cavity structure 202, a
structure that can include one or more optical cavities with
features described above. In system 200, at least one of the
optical cavities in structure 202, represented schematically by
cavity 204, can contain an analyte, illustratively being provided
to cavity 204. The presence of analyte in cavity 204 affects the
output light provided by structure 202, and the analyte-affected
output light, represented by arrow 206, can then be photosensed
within detector 210. For example, detector 210 may include a
photosensing component with one or more photosensitive surfaces at
which lateral variation of light is detected, such as after the
light passes through an LVF, which could, for example, be a tunable
LVF as described herein, possibly fabricated or attached directly
on one or more of the photosensitive surfaces. The sensing results
from detector 210 can be provided to other components within system
200 or to external components, as represented by arrow 212.
Detector 210 could be implemented in many different ways, such as
with a photosensing IC and a transmission structure which can, for
example, be a tunable LVF; features of photosensing ICs are
described in more detail in co-pending U.S. patent application Ser.
No. 11/702,250; entitled "Photosensing Optical Cavity Output Light"
and incorporated by reference herein in its entirety. The
implementation in FIG. 7 might, however, alternatively be
implemented with photosensing components that do not include
photosensing ICs, such as with one or more discrete
photodiodes.
Although cavity 204 can be any suitable type of homogeneous or
inhomogeneous optical cavity, including an emitting cavity or a
transmissive cavity, FIG. 7 illustratively shows one or more light
sources 220 that can be included within system 200 to illuminate
one or more optical cavities. As represented by arrow 222,
structure 202 receives input light from light sources 220. If
optical cavity 204 is illuminated as shown, the analyte-affected
output light represented by arrow 206 could include one or both of
transmitted and reflected light.
FIG. 8 illustrates electrical components that can be used in
implementing system 200 as in FIG. 7. System 200 illustratively
includes central processing unit (CPU) 240 connected to various
components through bus 242, but a wide variety of other
architectures could be employed, including any appropriate
combination of hardware and software, as well as specialized
hardware components such as application specific integrated
circuits (ASICs) for one or more of the illustrated components or
in place of a software component executed by CPU 240.
System 200 also includes component input/output (I/O) component
244, memory 246, integrated circuit input/output (IC I/O) 248, and
external I/O 249, all connected to bus 242. System 200 can include
various other components (not shown) connected to bus 242. In
addition to connections through external I/O 249 by which signals
can be provided to and received from external devices, bus 242 can
also be connected directly to components outside of system 200.
Component I/O 244 permits CPU 240 to communicate with certain
components of system 200, illustratively including illumination
control 250, cavity control 252, and analyte control 254. For
interactive applications, component I/O 244 could also be connected
to a suitable user interface, such as a monitor and keyboard (not
shown). In the exemplary implementation in FIG. 7, illumination
control 250 can include light sources 220 (FIG. 7) and circuitry
for controlling them; cavity control 252 can include electrodes or
other components that can be operated to control cavity 204 and
other cavities and can also include circuitry connected to those
components; and analyte control 254 can similarly include fluidic
devices or other components that can operate to transfer analyte
into, through, or out of cavity 204 or other cavities or to produce
relative movement between analyte and an array or a cavity, and can
also include circuitry connected to those devices and
components.
In the illustrated implementation of system 200, IC I/O 248 is a
similar I/O component that permits CPU 240 to communicate with one
or more ICs, such as in detector 210 in FIG. 5. M ICs are
illustrated by a series from IC(0) 260 to IC(M-1) 262, including
IC(m) 264 with a photosensor array 266.
Memory 246 illustratively includes program memory 270 and data
memory 272, although instructions for execution by CPU 240 and data
access during execution of instructions could be provided in any
suitable way, including through external devices or components. The
routines stored in program memory 270 illustratively include
analyte information routine 274. In addition, program memory 270
could store various additional routines and also subroutines (not
shown) that CPU 240 could call in executing routine 274. Similarly,
the data in data memory 272 illustratively include calibration data
276, but could include various additional items of data and data
structures accessed by CPU 240.
In executing routine 274, CPU 240 can provide signals to cavity
control 252 and to analyte control 254 so that an analyte is
present in cavity 204, for example, with the analyte having optical
characteristics that affect output light from cavity 204. CPU 240
can also provide signals to illumination control 250 so that cavity
204 is appropriately illuminated to provide analyte-affected output
light. CPU 240 can also provide signals to each of ICs 260 through
262 to obtain sensing results that include information about the
analyte in cavity 204. In an implementation with a
position-sensitive detector (PSD), CPU 240 could instead provide
whatever signals are necessary to obtain photosensed quantities
from the PSD; for example, CPU 240 could control circuitry to
connect output currents from the PSD to a differential
amplifier.
FIG. 9 illustrates one example of how analyte information routine
274 could be implemented in a system like system 200 in FIGS. 7 and
8. The routine in FIG. 9 could be implemented for single objects
moving along paths through cavities past arrays; for spaced
multiple objects moving along paths through cavities past arrays;
or for continuous streams of objects, such as small volumes of
fluid, moving along paths through cavities past arrays, in each
case subject to appropriate constraints and with the cavities
providing output energy distributions that include information
about analytes in objects, such as laterally varying energy
distributions if an inhomogeneous cavity.
Examples of objects that could occur in implementations as
described herein include droplets, bubbles, small volumes of fluid,
single molecules, agglomerated molecules, molecule clusters,
biological cells, viruses, bacteria, proteins, DNA, microparticles,
nanoparticles, and emulsions. A droplet or small volume of fluid
may, for example, include atoms, molecules or other particles that
affect refractive index, absorption, or other optical
characteristics. An object "travels" or is caused "to travel" if
the object moves through a succession of positions. For example,
the object could be conveyed in a fluid, such as a liquid, gas, or
aerosol, in which case the object may be referred to as being
"carried by the fluid."
The term "path" is used herein to refer to a substantially
continuous series of positions through which an object may travel.
A path is "through a cavity" if an object following the path passes
through part of the cavity. A photosensing component, such as an
array or PSD, is "positioned along" or "along" a path through a
cavity if the component is positioned near the cavity in such a way
that, when an object following the path affects output light from
the cavity, the photosensing component can obtain sensing results
that include information about how the object is affecting the
output light; it is not necessary, however, that the photosensing
component be immediately against or adjacent to an external surface
of the cavity that includes the path--there could, for example, be
another optical cavity or other optical component between them,
such as an LVF, which could be implemented as a tunable LVF as
described herein. An object following a path in a case where an
array is along the path in any of these ways can be said to move
"past the array".
The routine in FIG. 9 follows a general strategy of performing a
series of readout operations, after which information is combined
and provided. It would also be possible to provide the information
from each readout operation immediately or to provide information
both immediately after each readout operation and also after a
series of readout operations.
When CPU 240 executes the operation in box 300, it performs a
pre-sensing readout. The purpose is to obtain information necessary
to later perform a sensing readout. The information could be
obtained in the ways described in co-pending U.S. patent
application Ser. No. 11/315,992, entitled "Sensing Photons from
Objects in Channels" and incorporated herein by reference in its
entirety.
Using the information from box 300, CPU 240 could obtain
information about each object and determine an appropriate sensing
period for each object, in the operation in box 302. For example,
CPU 240 could perform calculations to determine whether one or more
objects are present, the position of each object, and the speed of
each object. Using this information and taking into account
previously calculated sensing periods for the same objects, if any,
CPU 240 can also determine an appropriate sensing period to be used
during sensing readout; in general, the sensing period must provide
an integration time shorter than the time necessary for an object
to pass each cell in an array. Each object can therefore have a
unique sensing period.
The operation in box 302 can also include providing any necessary
signals through component I/O 244 to adjust movement of objects,
such as by adjusting fluid speed; to adjust illumination or
stimulation of the optical cavity; or to adjust characteristics of
the optical cavity, such as by adjusting optical distances and/or
tilt angles between light-reflective components using techniques as
described herein. These signals could include any appropriate
combination of signals to illumination control 250, cavity control
252, and analyte control 254. In particular, these signals could
include providing tuning signals to a tuning structure to move
light-reflective components relative to each other, as described
above in relation to FIG. 1. Tuning signals could be provided to
move light-reflective components to a distance from each other at
which the optical cavity provides light with desired wavelengths or
with desired transmission or reflection modes. Tuning signals could
also be provided to tilt or otherwise modify orientation or, more
generally, relative positions of light-reflective components to
obtain a desired energy output function for an inhomogeneous
optical cavity.
If the tuning structure includes electrodes as described below, the
operation in box 302 can also include providing and monitoring
signals to measure capacitance between electrodes, which provides
information about distance between the electrodes. For example, CPU
240 could compare the measured capacitance with a fixed set
point.
CPU 240 can then cause operation of the cavity in a way that
encodes information about the analyte's optical characteristics and
can also perform sensing readout on a cavity's output light to
obtain photosensed quantities that depend on the output light's
intensity distribution, in box 304. This operation includes
providing any further signals through component I/O 244 so that the
cavity provides analyte-encoded output light and also providing
signals through IC I/O 248 so that photons are photosensed
cumulatively during the sensing period obtained in box 302. This
operation can also include providing signals through component I/O
244 to encode particular kinds of information about analyte optical
characteristics, such as to directly encode absorption spectrum
derivative or refractive index dispersion derivative by
continuously modulating cavity thickness during measurement or to
encode values at a series of sampling points by gradually scanning
the cavity across a range of wavelengths at discrete intervals or
in small increments that approximate a continuous scan, as could be
useful in obtaining a spectrum. Furthermore, cavity thickness
and/or tilt could be modulated periodically to obtain lock-in with
a readout signal having the same modulation frequency, to improve
signal-to-noise ratio and increase sensitivity, as described
below.
If the tuning structure includes electrodes as described below, the
operation in box 304 can also include providing and monitoring
signals to measure capacitance between electrodes, which provides
information about distance between the electrodes. For example, CPU
240 could compare the measured capacitance with a fixed set point,
or could monitor periodic or other variations in capacitance to
optimize measurements.
During this operation, CPU 240 may also provide signals to
peripheral circuitry on an IC so that analog quantities photosensed
by cells are adjusted based on reference values. After adjustment,
if any, analog quantities can be converted to digital signals for
readout. The operation in box 304 can be implemented in whatever
manner is appropriate for a given photosensing IC, whether a CCD or
CMOS implementation, and regardless of whether readout is purely
serial or is also parallel.
Since an analyte's optical characteristics can affect the output
light provided from a mode of an optical cavity, such as in the
ways described above in relation to FIGS. 3 and 5, information
about the optical characteristics is present in the cavity's output
light, encoded in intensity functions of one or more modes and in a
laterally varying energy distribution. Sensing results obtained in
box 304 can therefore include part or all of the encoded
information, in the form of photosensed quantities that depend on
the analyte's optical characteristics. For example, the sensing
results can include information about at least one of position,
size, and intensity of a light spot and, accordingly, about the
respective mode's intensity peak. If the output light from the
cavity includes intensity peaks for two or more modes, their
respective light spots can be tracked separately as described
below.
The photosensed quantities read out in box 304 can also be
digitally adjusted by CPU 240 before being stored for each object
and mode, in box 306. The digital adjustment can include adjusting
quantities photosensed by cells based on reference quantities or
based on calibration data 276 (FIG. 8), and can also include any
necessary adjustments due to differences in sensing periods or
other factors; calibration-based techniques that can be used are
described in co-pending U.S. patent application Ser. No.
11/633,302, entitled "Position-based Response to Light" and
incorporated herein by reference in its entirety.
The digital adjustment in box 306 and the analog adjustment, if
any, in box 304 can also employ reference cell-based adjustment
techniques described in co-pending U.S. patent application Ser. No.
11/316,438, entitled "Photosensing Throughout Energy Range and in
Subranges" and incorporated herein by reference in its entirety;
such reference cell-based adjustment techniques may be especially
useful for intensity referencing and in tracking an object's
position. In particular, such adjustments can be used to overcome
problems with inhomogeneous illumination, but such techniques may
be difficult to implement successfully in system 200 because
external inhomogeneities that affect output light, such as in
illumination or in stable or time-varying absorption by particles
between light sources 220 and optical cavity 204, are not readily
distinguishable from absorption within cavity 204. In other words,
adjustment based on reference cells may remove desired information
about absorption changes inside cavity 204.
To avoid this and other such problems, the operation in box 306 or
a subsequent operation can make an alternative data manipulation or
adjustment to obtain "cavity-only absorption data", an expression
that refers herein to values or other data in which information
about absorption in cavity 204 is preserved while information is
reduced about features exterior to cavity 204 such as
inhomogeneities in illumination and external absorption, operating
as described in co-pending U.S. patent application Ser. No.
11/702,249, entitled "Obtaining Information From Optical Cavity
Output Light" and incorporated herein by reference in its entirety.
As will be understood, the encoding of absorption information in
the manner described allows removal of noise-like effects other
than those from absorption coefficient inside cavity 204,
influences such as external perturbations, disturbances, or
inhomogeneities. As a result, measurements of absorption can have a
higher signal to noise ratio. Also, information can be recovered
from analyte-encoded output light that is selectively sensitive to
absorption changes inside cavity 204.
Other adjustment techniques that can be used, such as in box 306,
are described in co-pending U.S. patent application Ser. No.
11/702,329, entitled "Implanting Optical Cavity Structures" and in
co-pending U.S. patent application Ser. No. 11/702,325, entitled
"Containing Analyte in Optical Cavity Structures", both of which
are incorporated herein by reference in their entireties.
Orientation of components can result in non-perpendicular incidence
of input light on optical cavities, such as if an operation in one
of boxes 302 and 304 changes the tilt of the entry surface at which
a cavity receives incident light. Unless all output light is
incident on one position of the detector component or the detector
component has only a single large area as with some PSDs,
adjustments can be made to correct for non-perpendicular incidence
of input light: For example, if the light source component emits
light from a point source at many different angles that are
accordingly transmitted through the cavities at various angles, the
detector component's photosensitive surface receives the output
light at many different angles, but each cell of a photosensor
array would receive only a very small angular distribution;
therefore, if the angle could be known, as would be the case in a
fixed geometry but may not be the case in FIG. 7, the angle-induced
variation can be easily corrected.
The position and speed information about each object from box 302
can be used by the operation in box 306 to determine which
photosensed quantities result from effects of each object. Similar
techniques can be used to determine which photosensed quantities
result from each mode's light spot when a cavity's output light
includes two or more modes.
For homogeneous analyte in cavity 204 or for stationary or
slow-moving objects in cavity 204, lock-in techniques could be
applied to further improve signal to noise ratio, such as by
modifying operations in boxes 302, 304, and 306 in FIG. 9. For
example, illumination from light sources 220 can be modulated in
order to modulate output light from cavity 204. Or, as described
above, cavity thickness and/or tilt can be modulated, in effect
modulating characteristics of the cavity. The applicable modulation
frequencies would be constrained by the readout frequency
achievable by detector 210; rapid readout may be available, for
example, with photosensing components that provide differential
signals in response to position changes on a photosensitive
surface, some examples of which are described in greater detail in
co-pending U.S. patent application Ser. No. 11/633,302, entitled
"Position-based Response to Light" and incorporated herein by
reference in its entirety--differential signal techniques may also
have very high sensitivity as could be necessary to determine
extremely small refractive index changes of analyte in a cavity. In
implementations where it is not possible to directly record a
correlation signal, another type of reference could be used, such
as an empty channel in a fluidic structure, a channel with a
reference medium, or an uncoated reference cell in a photosensing
array with coated cells to sense photon energy subranges.
In performing the operations in boxes 304 and 306, CPU 240 can
employ data structures (not shown) stored in memory 246. For
example, one data structure can store each object's previously
calculated position and speed, which can then be used in performing
subsequent calculations to identify effects of the same object;
similarly, each object's data structure can also include each light
spot's identifying information and the object's effect on the
identified light spot, which can similarly be used in subsequent
calculations. Also, a readout data structure can be employed to
hold all of the adjusted quantity information about each
object.
The operation in box 306 can update the readout data structure each
time it obtains additional information about the same object. In an
implementation as in FIG. 8, the operations in boxes 300, 302, 304,
and 306 can be performed separately for each of ICs 260 through
262. Further, as suggested by the dashed line from box 306 to box
300, the same operations can be performed repeatedly for each of
the ICs. If each object can be correctly identified throughout its
travel along a path through cavity 204, the readout data structure
can be used to hold all of the information obtained from all ICs.
Between consecutive executions of the operations in boxes 300, 302,
304, and 306, the effects of each object may move only a few cells
along the path, and consecutive objects must be sufficiently
separated to avoid confusion. For example, each object may be a few
.mu.m in diameter, each cell may have a length along the path of
between 10 and 20 .mu.m, and consecutive objects may be two or
three cell lengths apart. For larger objects or for cells of
different sizes, the spacing between consecutive objects can be
adjusted appropriately.
Various modifications could be made in the implementation of FIG.
9. For example, rather than being spaced apart, objects could be
closer together. Even if several objects are having overlapping
effects on a light spot, it may be possible to perform
computational algorithms to separate the effects of the objects.
Similarly, if objects are very close to each other but positioned
along different cells, an optical structure between the path of the
objects and detector 210 could ensure that photons affected by
different objects travel to different cells; in this way, a
continuous stream of objects could be measured. Furthermore,
techniques as described above could be applied to a continuous
fluidic stream without distinguishable objects in it, in which case
the analyte-affected output light from optical cavity 204 would be
determined by optical characteristics of concentrations of
molecules in each position in the stream rather than by optical
characteristics of distinguishable objects. In effect, the stream
would be divided into imaginary small volumes, each of which would
be an object analyzed as described above, allowing for continuous
monitoring of how the output light from the fluid changes with
time, such as due to changing composition of the fluid.
As the operations in boxes 300, 302, 304, and 306 are repeated
while an object travels along a path past detector 210, more and
more information is obtained, especially where a cavity's output
light has more than one light spot, with each light spot having a
respective position on the array. When the object has passed the
whole array, information about the analyte it contains can be
recomposed from the stored fractions.
Upon completion of any suitable amount of information gathering in
boxes 300, 302, 304, and 306, CPU 240 can perform the operation in
box 310 to provide analyte information, such as in the form of data
for another routine or as output through external I/O 249. As
shown, this operation can include combining the sensed quantities
for each object so that analyte information for the object can be
provided, such as in the form of an absorption spectrum, a value
for the analyte's refractive index, or some other data structure.
Further description of information obtaining techniques is provided
in co-pending U.S. patent application Ser. No. 11/702,249, entitled
"Obtaining Information From Optical Cavity Output Light" and
incorporated herein by reference in its entirety.
Many possible uses exist for analyte information as obtained in box
310, and operations like those in FIG. 9 could be implemented with
a wide variety of existing technologies; analyte information could
be used, for example, to distinguish objects, as described in
detail in co-pending U.S. patent application Ser. No. 11/702,328,
entitled "Distinguishing Objects" or to detect glucose in bodily
fluids, such as with techniques described in co-pending U.S. patent
application Ser. No. 11/702,329, entitled "Implanting Optical
Cavity Structures", both of which are incorporated herein by
reference in their entireties. Furthermore, it is foreseeable that
further uses of analyte information and technologies for
implementing such operations will be developed in the future. In
general, analyte information from box 310 can be used in any way
whatsoever, including not only existing techniques but also
techniques developed hereafter. The operations illustrated in FIG.
9 do not require any specific technology, such as for data storing
or processing operation, and are compatible with any such
technology that exists now or may be hereafter developed.
FIG. 10 shows device 350, which can also be used in a system as in
FIGS. 7 and 8. Light-reflective components 352 and 354, together
with the region between them, can operate as an inhomogeneous
optical cavity as shown when illuminated by input light,
represented by arrows 356.
Components 352 and 354 have electrodes 360 on their inward
surfaces, facing each other and with deformable spacers 362 and 364
between them; electrodes 360 can, for example, be metal or other
conductive material. As a result, signals can be provided to
electrodes 360 to cause changes in distances between the inward,
reflective surfaces of components 342 and 344, such as
electrostatically, electromagnetically, or piezoelectrically,
changing the shape of the region between them, as suggested by
angle 366. For example, one or both of the electrodes 360 at the
ends of each of spacers 362 and 364 can be independently
addressable from those at the ends of the other spacers, so that
each spacer can be independently deformed, such as to change angle
366 or change optical thickness of the cavity. In exemplary
electrostatic implementations in which spacers 362 and 364 include
dielectric elastomer material, voltage signals can cause attraction
and repulsion between electrodes 360 and also electrostrictive
forces in the elastomer, in turn causing deformation of spacers 362
and 364; in microelectromechanical systems (MEMS) switch
implementations, however, one electrode in each pair is usually
grounded while the other can be charged with either polarity to
produce attraction (but not repulsion)--the resulting deformation
brings the pair of electrodes toward each other, and when
attraction ends they then move away from each other due to
elasticity. In exemplary electromagnetic implementations in which
spacers 362 and 364 include nonmagnetic elastomer material, each of
electrodes 360 includes an embedded or otherwise attached
electromagnet (not shown) oriented and electrically connected so
that electrical signals through electrodes 360 can produce
attraction and repulsion between electromagnets, similarly causing
compression or expansion of spacers 362 and 364. In exemplary
piezoelectric implementations in which spacers 362 and 364 include
piezoelectric material, spacers 362 and 364 contract or expand in
response to electrical signals received through electrodes 360. In
addition to these examples, deformable components with various
other materials could be implemented.
An independent voltage signal could be applied to each electrode to
cause a desired deformation, with the specific signal depending
both on the deformation and also on the manner in which deformation
is produced; alternatively, one or more larger electrodes could be
at one side of the cavity, and independent voltage signals could be
applied to smaller electrodes on the other side, to different parts
of each larger electrode, or in a delay-line technique that would
propagate across each larger electrode. Calibration as described
below could be performed to determine the specific voltage required
across a given electrode pair to produce a specific distance
between the electrodes, and the results could be included in
calibration data 274 (FIG. 8). Since the distance between
electrodes corresponds closely with cavity thickness and since
cavity thickness determines the range of transmitted wavelengths,
calibration can be based on transmitted wavelengths rather than
actual measurements of cavity thickness. In addition to transmitted
wavelength, tuning can also control other optical characteristics
of the optical cavity, including FSR, LVF gradient, and so
forth.
In one experimental implementation, a layer of polydimethylsiloxane
(PDMS) elastomer (which can be spin-coated up to 100 .mu.m, a
process that can also control surface roughness and flatness of
metal mirror layers) was subjected to a voltage between highly
reflective metal electrodes on its opposite sides, simulating an
implementation with a single uniform spacer rather than separate
spacers as in FIG. 10; a single spacer could be used because PDMS
is transparent in the visible and infrared ranges, similarly to
glass, so that it can be the light-transmissive region of an
optical cavity. PDMS elastomer is incompressible with a modulus of
elasticity approximately 0.5 MPa, but voltage across a PDMS layer
causes electrostriction in the elastomer. In a 5 .mu.m thick layer,
220 V caused a thickness deformation of 200 nm, corresponding to a
4% change in cavity thickness and therefore approximately 4% shift
of the Modes of a Fabry-Perot interferometer or etalon, e.g. from
686 nm to 713 nm.
The above experimental implementation demonstrates that widely
tunable cavities can be fabricated with elastomer spacers between
light-reflective components. Furthermore, with different
dimensions, both in thickness and lateral extent, and with
different elastomer material, even larger relative deformations
should be achievable. Because the voltage needed to induce a given
deformation depends on various factors including spacer thickness
between electrodes, electrode quality, and the elastomer material
used, it should be possible to reduce the required voltage
significantly through optimization.
With independently addressable electrodes, device 350 can be tuned
in a wide variety of ways: Tilt angle 366 can be increased to allow
additional Fabry-Perot modes in an LVF; tilt angle 366 can be
reduced to narrow the transmission range of an LVF, up to the limit
in which it operates as a homogeneous cavity; tilt angle 366 can
similarly be adjusted to accommodate a specific narrow band light
source; thickness can be adjusted uniformly to shift the cavity's
range; and so forth.
The distances between electrodes in each pair, indicative both of
cavity thickness and of the angle of tilt, can be very precisely
measured and controlled, such as by capacitive measurement,
allowing adjustment of device 350 for a particular application and
also allowing use of lock-in techniques. For this purpose, too, it
is useful that the electrodes at the ends of each spacer are
independently addressable. It would also be possible to have
additional electrodes dedicated to obtaining capacitance
measurements to measure distances between electrodes.
At positions where photon energy of input light is the same as a
transmission mode of device 350, light is transmitted to
photosensing component 368, which obtains sensing results. If
analyte is present in the region between structures 6352 and 354,
optical cavity operation can provide analyte-affected output
light.
In the implementation illustrated in FIG. 10, light-reflective
component 354 is shown directly on photosensing component 368,
suggesting that component 354 could be fabricated directly on top
of a photosensitive in a photosensing IC such as a photosensing
array or a PSD, which could produce a very compact detector. In
general, however, component 354 could be fabricated on a substrate,
such as a glass slide, and one or more optical components could
also be positioned between the substrate and photosensing component
368, to produce a desired light distribution on one or more
photosensitive surfaces in photosensing component 368, as described
in more detail for optical cavities that contain fluid analytes
such as liquid, gas, or aerosol in co-pending U.S. patent
application Ser. No. 11/702,325, entitled "Containing Analyte In
Optical Cavity Structures" and incorporated herein by reference in
its entirety.
FIG. 11 illustrates an example of how device 350 can be adjusted to
obtain two different transmission spectra. The intensity-energy
graph in FIG. 11 includes two curves: The curve that includes peaks
380 results from a spacing of 4.8 microns between structures 352
and 354, while the curve that includes peaks 382 results from a
spacing of 5 microns. Mirror reflectivity of 95% was used. The
resulting wavelength shift of approximately 30 nm corresponds to a
relative change of the cavity thickness which is similar to the 4%
shift obtained experimentally, as described above. Although these
curves indicate operation of device 350 as a homogeneous optical
cavity, similar results would occur if it were operated as an
inhomogeneous cavity as illustrated in FIG. 10, though an
intensity-position graph would be more appropriate in that case. In
either case, the output light could include information about
optical characteristics of analyte in the region between structures
352 and 354, encoded as described above in relation to FIGS. 3 and
5.
The techniques in FIGS. 10 and 11 can be extended to obtain
derivatives directly by recording mode intensity while continuously
changing cavity thickness. Similarly, cavity shape can be adjusted
by such techniques to improve sensitivity; for example, sensitivity
can be further increased if cavity thickness is periodically
modulated with a small amplitude, also referred to as "wobbling",
during continuous change of cavity thickness.
A device as in FIG. 10 can also be used for other purposes, such as
to produce an optical cavity or transmission structure with desired
characteristics. For example, an inhomogeneous optical cavity with
desired optical thickness could be produced; similarly, a
transmission structure that is an LVF with a desired gradient could
be produced.
Tunable inhomogeneous cavities could be implemented in many ways
besides the way illustrated in relation to FIGS. 10 and 11.
FIG. 12 shows device 400, which can also be used in a system as in
FIGS. 7 and 8. Light-reflective components 402 and 404 provide
reflection surfaces on either side of region 406, which can be
filled with analyte as shown. By operating deformable components as
described above in relation to FIGS. 1 and 10, light-reflective
components 402 and 404 can be moved relative to each other, such as
to change their relative orientations or "tilt angle", as suggested
by dashed outline 408, illustrating a different position of
component 404 relative to component 402. As described above, the
distance between components 402 and 404 could similarly be
changed.
FIG. 12 also shows photosensing component 410, which could be
implemented as part of device 400 with or without one or more
optical components between light-reflective component 404 and
photosensing component 410, such as in the way illustrated in FIG.
10 or in the ways described in greater detail in co-pending U.S.
patent application Ser. No. 11/702,325, entitled "Containing
Analyte In Optical Cavity Structures" and incorporated herein by
reference in its entirety. Alternatively, photosensing component
410 could be part of a separate device, such as in some of the
techniques described in co-pending U.S. patent application Ser. No.
11/702,329, entitled "Implanting Optical Cavity Structures" and
incorporated herein by reference in its entirety.
When device 400 receives input light, represented by arrows 412,
through component 402, optical cavity operation can occur,
resulting in transmission of analyte-affected output light to
photosensing component 410; if appropriate, an LVF or other optical
components could be positioned between light-reflective component
404 and photosensing component 410, such as for the reasons
described in co-pending U.S. patent application Ser. No.
11/702,250, entitled "Photosensing Optical Cavity Output Light" and
incorporated by reference herein in its entirety. The index of
refraction of analyte in region 406 and the relative positioning of
components 402 and 404 determine positions of light transmission,
and illumination can be provided so that only one wavelength is
transmitted but at varying output light positions, two of which are
represented by arrows 414 and 416: Arrow 414 could, for example,
represent output light provided when components 402 and 404 are in
the position illustrated by component 404, while arrow 416 could
represent output light provided when in the position illustrated by
dashed outline 408.
FIG. 13 shows a similar example of the pattern of light on the
upper surface of photosensing component 410 if the optical cavity
were illuminated in only one narrow wavelength band. As shown,
light spot 420 on photosensing component 410 indicates that the
incident narrow band light is transmitted at a certain position
Xtrans1. If the shape of the optical cavity changed due to movement
of light-reflecting component 404, such as to the position of
outline 408, the location of the transmitted light spot 420 would
move, either toward Xmin, as shown by light spot 422 at Xtrans2, or
toward Xmax. If analyte absorption changes, causing a change in
intensity, contrast, and FWHM of output light's intensity function,
the size and intensity of light spot 420 would change rather than
its position.
Tunable inhomogeneous optical cavities can be implemented in many
ways in addition to the way illustrated in FIGS. 12 and 13. In many
applications, an optical cavity structure as in FIG. 7 could be
implemented to include one or more tunable inhomogeneous optical
cavities that contain analyte as in FIGS. 12-13.
FIG. 14 illustrates exemplary operations in producing a device like
devices 350 (FIG. 10) and 400 (FIG. 12). In particular, the
operations in FIG. 14 make it possible to produce apparatus in
which a tunable inhomogeneous optical cavity occurs in a coating on
top of a photosensing IC, allowing increased sensitivity and
compactness of an optical sensor of analyte optical
characteristics.
The operation in box 500 in FIG. 14 produces entry and exit partial
optical cavity structures, with suitable parts to provide
deformable spacers and electrodes for controlling cavity shape.
This operation can include producing an entry light-reflective
component, with or without a substrate such as an entry glass, and
also producing an exit light-reflective component, again with or
without a substrate such as an exit glass, with electrodes and
deformable spacers fabricated photolithographically on one or both
of the light-reflective components. Prior to fabricating the
electrodes and spacers, this operation can include producing an
entry light-reflective component on an entry glass (or directly on
a light source such as an LED) and also producing an exit
light-reflective component on an exit glass (or directly on a
photosensitive surface, such as of a photosensing array or PSD).
This operation can also include producing a patterned layer of a
deformable material, e.g. an elastomer such as SU-8 or
polydimethylsiloxane (PDMS), on one or both of the light-reflective
components, such as with techniques described in co-pending U.S.
patent application Ser. No. 11/315,992, entitled "Sensing Photons
from Objects in Channels" and incorporated herein by reference in
its entirety.
A patterned layer of elastomer or other deformable material could
include structures that operate as spacers and walls, dimensioned
and positioned to ensure that the resulting deformable components
are capable of operating as desired, and with a desired degree of
elasticity if appropriate. For example, a single piece of elastomer
could be formed with a duct or channel running through it or with a
well defined in one of its surfaces to receive analyte, or one set
of elastomer parts could operate as spacers controlled by
electrodes and another set could operate to bound ducts, channels,
wells, or other bounded analyte regions.
In an alternative approach, electrodes and elastomer spacers could
be fabricated on one of the light-reflective components and a
second set of electrodes could be fabricated on top of the spacers;
unless the second set of electrodes or other parts of the same
layer also provide sufficient reflectivity, the other
light-reflective component could then be placed on top of the
second set of electrodes. In experimental implementations of this
approach with a single elastomer spacer and silver
mirror/electrodes, the first mirror/electrode has high
reflectivity, but the second mirror/electrode has between
approximately 60% and 80% reflectivity, apparently due to materials
used and fabrication process; it is expected that a compromise can
be reached by sacrificing voltage response to achieve higher
reflectivity by using of Sylgard 182 elastomer with less or no oil,
by using other elastomer materials, by using metal transfer
processes for the second mirror/electrode or by making other
changes in materials or processes.
The material used in box 500 to produce deformable components can
be an elastomer, i.e. an elastic substance resembling rubber, or
other deformable material chosen so that it responds appropriately
to the operation that causes deformation, whether an electroactive,
electrostatic, electromagnetic, magnetic, piezoelectric,
mechanical, or other type of operation. If the material also has
surfaces that bound and define ducts, channels, wells, or other
regions to contain analyte, as suggested in FIG. 1, material can be
chosen that is compatible with expected characteristics of analyte,
including pH, viscosity, likely reactions with materials, and so
forth. If appropriate, an anti-adhesive coating can be applied to
interior duct, channel, or well surfaces, such as by dip-coating
polyethylene glycol (PEG) or by providing a coating of parylene C
or vapor deposited tetraglyme, and the choice of coating must also
be compatible with the deformable material.
In another approach, the operation in box 500 can be implemented
using an elastomer, gel, or oil between the mirrors in a
silicon-based MEMS or piezoelectrically controlled tunable cavity
to increase tuning range. In this case, the elastomer's
electroactive property would not be used, but the elastomer would
increase refractive index. If a liquid is used, the liquid and the
movable mirror can be moved in various ways, such as by using PZT
to produce a traveling wave in the liquid.
The operation in box 502 then attaches the entry and exit partial
structures, with attached fluidic components to position analyte in
the resulting optical cavity. The operation in box 502 can include
forming a suitable bond between the entry and exit partial
structures so that they are firmly attached to each other. Also,
the fluidic components attached to the resulting optical cavity
structure can include, for example, connectors, tubing, pumps,
sensors, and so forth; it is important that the combination of
fluidic components be capable of operating to cause and control
positioning of analyte within the optical cavity, such as by
carrying the analyte into the optical cavity with a fluid or in
some other way. The operation in box 502 can also optionally
include attachment of wires or other appropriate circuitry
connected, for example, to the photosensing array.
The operation in box 504 then attaches any other additional
components necessary to complete the device. For example, if the
device includes light sources, these components can be attached by
the operation in box 504. Similarly, if a photosensing array is not
part of the exit partial structure, a photosensing component can be
attached by the operation in box 504. The operation in box 504 can
also include any other external electrical, optical, or fluidic
connections necessary for operation of the device, including any
necessary connections from external circuitry to electrodes to
control elastomer, as shown. Alternatively, such connections could
later be made when the device is incorporated into a system, such
as system 200 in FIGS. 7 and 8.
The choice of a detector can be made based on several constraints.
For example, if intensity peaks of a small number of modes are
photosensed to detect changes in central energy or position,
amplitude, contrast, and FWHM, it may be possible to use a
respective one-dimensional photosensing array for each optical
cavity, with each array including a relatively small number of
cells, reducing the electrical power requirement because less power
is dissipated in the detector. In general, compactness is promoted
by using a photosensing IC, as described in co-pending U.S. patent
application Ser. No. 11/702,250, entitled "Photosensing Optical
Cavity Output Light" and incorporated by reference herein in its
entirety.
The operation in box 506 can be performed at any appropriate time
after the other operations, as suggested by the dashed line from
box 504 to box 506. In addition, the operation in box 506 performs
calibration, which requires that components be appropriately
connected to circuitry, such as in the ways illustrated in FIGS. 7
and 8. The necessary connections could be created as part of the
operations in boxes 500, 502, and 504 or instead could be created
after the operation in box 504 and before performing calibration.
In any case, calibration in box 506 can include obtaining items of
data or data structures to be used in obtaining analyte information
as described herein, and the data or data structures can be stored
in memory 246 as part of calibration data 276 (FIG. 8), or, in
appropriate cases, can be embedded in analyte information routine
274 or stored in another appropriate form.
A typical fabrication process that roughly follows boxes 500, 502,
504, and 506 and that should be simple and cheap and would allow
fabrication as in FIG. 10 of an optical cavity structure directly
on top of a photosensitive surface, such as of a photosensing array
or a PSD, could proceed as follows: First, a dielectric or metal
mirror (that may also include bottom electrodes) Is formed by
deposition of material on a substrate or on top of the
photosensitive surface; if a dielectric mirror is used or if
otherwise necessary or desirable such as to separately optimize
mirror and electrode performance, a conductive layer is then
deposited and photolithographically patterned to form bottom
electrodes for the spacers; an elastomer layer is then formed and
patterned to form spacers, such as by spin casting and structuring
PDMS on top of the bottom electrodes; top electrodes are then
formed on top of the spacers, such as by depositing and
photolithographically patterning another conductive layer; and then
a second dielectric or metal mirror is attached over the top
electrodes, stabilized if necessary by an appropriate
substrate.
The typical fabrication process described above can be modified for
various specific purposes. For example, the top and/or bottom
electrode layers can be patterned photolithographically to provide
individual addressing of electrodes. Also, a specific thickness of
elastomer can be used that allows desired cavity thicknesses. After
both sets of electrodes have been formed, they can be connected and
spacers can be adjusted by tuning the cavity in situ during the
fabrication process; for example, the cavity can be illuminated by
a homogeneous, parallel narrow band light source and adjustment can
be made to obtain a desired interference pattern in the output
light, photosensed by a camera,
After in situ tuning, cavity thickness can be fixed with glue or
epoxy, potentially in combination with a spacer material exhibiting
low thermal expansion coefficient, such as Zerodur. Before sealing
the cavity completely, it may be advantageous to fill parts of the
cavity that will not contain analyte with a high-index medium in
order to minimize dependence of its characteristics on angle of
incident light.
For a cavity that can be further tuned after fabrication is
completed, a coarse fabrication can first be performed as described
above, such as by tuning voltages across the spacers to get desired
capacitances between measurement or control electrodes. After
fabrication, a calibration operation as in box 506 could correlate
voltage settings with optical properties. This approach could be
employed both for a cavity on a substrate and for a cavity
integrated on top of a photosensitive surface of a photosensing
component.
In general, the operations in any of boxes 500, 502, 504, and 506
can include additional activities. For example, at any appropriate
point in production of the device, wires or other appropriate
circuitry can be attached to provide signals to or from a
microprocessor or input/output (I/O) device to pumps and other
fluidic components or to provide signals from a photosensing array
to a microprocessor or I/O device. Similarly, connections can be
made at any appropriate time to provide power.
The technique of FIG. 14 could be modified in many ways within the
scope of the invention. For example, the operations in boxes 500,
502, and 504 could be combined in any appropriate way to facilitate
attachment of components in a desired sequence. Also, an additional
operation could be performed to align or attach interconnects
between ICs, gates, and other circuitry, such as connectors to a
microprocessor or computer, or this operation could be partially
performed in each of boxes 500, 502, 504, and 506. Furthermore, the
technique of FIG. 14 is extremely general, and could be employed to
produce a wide variety of different devices that encode information
about optical characteristics of analyte within an optical cavity
and obtain sensing results indicating the optical characteristics.
Examples described above show how objects can be carried through a
channel within an optical cavity while such operations are
performed, but various other arrangements are possible, some
examples of which are described below.
Some of the implementations described above in relation to FIGS.
1-14 are examples of optical cavity devices that include first and
second structures that can move relative to each other and,
connected to the first and second structures, a set of one or more
tuning structures. The first and second structures include first
and second light-reflective components, respectively, and the
device also includes an inhomogeneous optical cavity between the
light-reflective components. The tuning structures can tune the
optical cavity by changing relative positions of the
light-reflective components. At least one of the tuning structures
includes first and second electrodes connected to the first and
second structures, respectively, and connectible to receive
electrical tuning signals. The tuning structure also includes a
deformable component between the electrodes that is deformable in
response to the electrical tuning signals.
In specific implementations, electrodes of each tuning structure
can be on facing surfaces of the first and second structures,
respectively. A deformable component can include dielectric
elastomer material that is deformed in response to an electrostatic
field between electrodes; nonmagnetic elastomer material that is
deformed by electromagnetic attraction or repulsion between
electrodes; or piezoelectric material that expands or contracts in
response to electrical signals received through the electrodes. The
tuning structures, by changing relative positions of the
light-reflective components, can change the optical cavity's shape
by changing at least one of tilt angle and optical distance or
thickness.
In further specific implementations, the optical cavity can have an
exit surface and the device can include a photosensing component
connected to the exit surface to receive the output light. The
device can be a linear variable filter.
Some of the implementations described above in relation to FIGS.
1-14 also illustrate examples of systems that include an optical
cavity device as described above, sensing components that can sense
a feature of relative position of the light-reflective components
and provide feature signals indicating the sensed feature, and
control circuitry that receives the feature signals and, in
response, provides the electrical tuning signals.
In specific implementations, the control circuitry can include a
processor that provides the tuning signals based on the feature
signals and also on calibration data. The sensing components can
sense distance between light-reflective components.
Some of the implementations described above in relation to FIGS.
1-14 also illustrate examples of methods of making optical cavity
devices. Such a method can include producing an optical cavity
device as described above, in which the optical cavity and the
tuning structures are produced so that at least one tuning
structure includes electrodes and a deformable component as
described above.
In specific implementations, during the act of producing the
optical cavity and tuning structure, the tuning structure is
operated to change the shape of the optical cavity to an initial
shape. The initial shape can be that of a linear variable filter.
The optical cavity can be illuminated by a known light source and
its output light can be photosensed, and the photosensing results
can be monitored while operating the tuning structure. Such a
method can also include fabricating the optical cavity device on a
photosensitive surface of a photosensing IC; in use, the
photosensitive surface would receive output light from the optical
cavity.
Some of the implementations described above in relation to FIGS.
1-14 also illustrate examples of methods of using an optical cavity
with a changeable shape. Such a method can tune the optical cavity
by changing its shape and operate the optical cavity to provide
output light with a laterally varying intensity distribution that
depends on the optical cavity's shape.
In specific implementations, the act of tuning can be performed
before operating the optical cavity. For example, the act of tuning
can determine a photon energy range in which the optical cavity
transmits light, and the output light can then be within the photon
energy range. The number of modes in which the cavity provides
output light can be changed.
In other specific implementations, tuning and operating are
performed concurrently. For example, the optical cavity's shape can
be continuously changed while it is operated. The output light can
be photosensed at a photosensitive surface and, in tuning, the
optical cavity's shape can be modulated at a frequency to perform a
lock-in operation. The optical cavity's shape can alternatively be
incrementally changed while it is operating.
In further specific implementations, the act of tuning and the act
of operating are performed alternately. For example, the act of
operating can include a series of operations during each of which
the optical cavity receives input light from a respective light
source; then, after each operation in the series, the optical
cavity's shape is changed for the next operation.
In further specific implementations, the method can also provide
input light to the optical cavity and photosense output light
provided by the optical cavity in response to the input light,
obtaining sensing results. In doing so, the method can provide
tuning signals causing the optical cavity to have a sequence of one
or more shapes. For each shape, the photosensed output light can
have a respective laterally varying intensity distribution, and the
sensing results can include information resulting from the
laterally varying intensity distribution.
In further specific implementations, a sequence of tuning signals
can be provided such that the sensing results indicate a derivative
of absorption or dispersion with respect to wavelength. The device
can have optical thickness that varies laterally, with the tuning
signals causing changes in lateral variations in optical thickness.
The photosensed output light can include a light spot on a
photosensitive surface, and the tuning signals can vary
periodically with a constant frequency, so that the light spot also
moves periodically with the same frequency. The photosensing
results can be used to obtain a differential quantity indicating
the light spot's position and a lock-in operation can be performed
to increase the precision of the light spot's precision as
indicated by the differential quantity. More generally, the
photosensing results can be used to obtain calibration data.
Some of the implementations described above in relation to FIGS.
1-14 also illustrate examples of methods of using an optical cavity
device with an inhomogeneous optical cavity. The device can respond
to tuning signals by changing the cavity's energy output function.
Such a method can provide input light to the device while
photosensing its output light to obtain sensing results. In doing
so, the method can provide tuning signals that cause the device to
have a sequence of laterally varying energy output functions, and
for each function, the photosensed output light can have a
respective laterally varying intensity distribution. The sensing
results can include information resulting from the intensity
distribution.
Some of the implementations described above in relation to FIGS.
1-14 also illustrate examples of systems that include a tunable
optical cavity device as described above, a photosensing component
with one or more photosensitive surfaces, and control circuitry
that operates the cavity. The control circuitry can provide tuning
signals causing the cavity to have a sequence of laterally varying
energy output functions as described above, and in response to each
function's output light, the photosensing component can provide
sensing results including information resulting from the intensity
distribution.
In specific implementations, the tunable optical cavity device can
include light-reflective components as described above and a
tunable structure as described above; in general, the optical
cavity can have energy output functions in sequence, each for a
respective position of the light-reflective components. The optical
cavity can be a graded etalon with approximately linear gradient,
which is changed when the tunable structure moves the
light-reflective components. The system can also include sensing
components and control circuitry as described above.
In further specific implementations, the control circuitry can
provide first tuning signals and then second tuning signals and can
receive sensing results after the first tuning signals which it
then uses to provide the second tuning signals. For example, the
control circuitry can provide the second tuning signals to obtain
more precise sensing results. The system can also include a light
source that provides input light to the cavity.
Some of the implementations described in relation to FIGS. 1-14
also illustrate examples of a method of producing an optical cavity
device that includes light-reflective components and a tunable
structure as described above. The method can also include
structuring the deformable component such that the tunable
structure, in response to the tuning signals, can move the
light-reflective components with a subrange of positions and, for
each position in the subrange, the optical cavity has a respective
laterally varying energy output function.
The implementations in FIGS. 1-14 illustrate various applications
of techniques as described above, including production and use of
various tunable inhomogeneous optical cavity devices with
adjustable spectral range and, for LVFs, adjustable gradient, with
the adjustments depending on the application and available both
during production and use. Such devices can be combined with
photosensing components that photosense output light from modes of
tunable optical cavities that contain analyte and obtaining
information about the analyte, such as about its refractive index
and absorption coefficient. The techniques could be readily
extended to obtain information about polarization and fluorescence.
More generally, tunable analyte-containing optical cavities, such
as Fabry-Perot interferometers or etalons, could be used to
selectively filter narrow wavelength bands from incident broadband
radiation in accordance with analyte optical characteristics; in
combination with a detector, such as one that includes a
photosensor array, a tunable optical cavity can be used as a
spectrometer. In general, tunable optical cavities as described
above are suitable for integration with other devices, such as
semiconductor devices, making them appropriate for a wide variety
of other applications, such as with individually addressable arrays
of Fabry-Perot cavities.
Techniques that obtain information about analytes, as exemplified
by the implementations in FIGS. 1-14, can be applied in many
measuring techniques. For example, fluidic sensing, e.g. liquid,
gas, or aerosol, could be performed with infrared illumination. For
these applications, a tunable optical cavity with features similar
to commercially available LVFs in the visible range might be
appropriate. Especially interesting spectral ranges for gas sensing
include 8 .mu.m to 14 .mu.m with 600 nm/mm gradient, and with the
mirror spaced at 12-20 .mu.m over 1 cm for a 3.lamda./2 cavity and
3 .mu.m to 5 .mu.m with 200 nm/mm gradient, and with the mirror
spaced at 4.5-7.5 .mu.m over 1 cm for a 3.lamda./2 cavity. Other
interesting ranges for sensing applications include the
mid-infrared (2-5 .mu.m) and long wave infrared (6-12 .mu.m).
Another potential area of application is in distinguishing objects
such as biological cells, such as by counting, sorting, and so
forth. Using a reference medium with no cells or objects in a
device can eliminate the influence of varying environmental
changes, as described in co-pending U.S. patent application Ser.
No. 11/702,329, entitled "Implanting Optical Cavity Structures" and
incorporated herein by reference in its entirety. Related
techniques could be used to obtain probability of a certain type of
object, such as cancerous cells. Also, for rare cell scanning, the
above techniques may be useful because they can provide high
throughput (counting/sorting speed): if a high number of parallel
channels can be used, e.g. 200, it may be possible to sort 1 out of
10,000,000 cells within a few seconds using a device with the
typical dimensions of a CMOS detector chip. Techniques for
distinguishing objects are described in greater detail in
co-pending U.S. patent application Ser. No. 11/702,328, entitled
"Distinguishing Objects" and incorporated herein by reference in
its entirety.
Another potential area of application is in implantable products
useful to obtain information about analytes such as glucose in
bodily fluids, as also described in co-pending U.S. patent
application Ser. No. 11/702,329, referenced above. Since typical
dimensions of a device as described are in the 3-12 .mu.m range,
such devices should be able to handle high water background
absorption in the 3 .mu.m as well as the 8-12 .mu.m range.
Various of the techniques described above have been successfully
implemented or simulated, including the production and operation of
chip-size detectors that include LVFs on photosensing ICs. The
influence of an analyte in the cavity of an etalon has been
experimentally tested and simulated. Prototypes of elastomer-based
devices with deformations up to 200 nm, approximately 4% of
elastomer thickness, have been demonstrated, and it appears that
further scaling is feasible using thicker or thinner films. In
particular, elastically deformable spacers with small lateral
dimensions are expected to allow for larger tuning ranges.
The exemplary implementations described above allow compact,
inexpensive components to rapidly and accurately perform operations
such as measuring optical characteristics of fluids, biological
cells, glucose, and other analytes. In particular, such
implementations make it possible to use deformable components that
operate both to change optical cavity characteristics, such as by
changing thickness and tilt, and also to bound, contain, or
otherwise define regions within the cavity that can contain
analyte. This approach provides greater flexibility than previous
techniques to control optical cavity thickness, such as with
piezoelectric or MEMS components. At the same time, the techniques
described above could be implemented in combination with
piezoelectric or MEMS components; for example, deformable
components such as spacers could be made from thin film
piezoelectric material.
A wide range of implementations is available with techniques
described above, making it possible to overcome problems with
previous approaches to tunable optical cavities. Compared to
proposed techniques that change refractive index of electro-optic
material in a cavity, it is possible to operate devices as
described above with lower voltages and larger tuning ranges. Also,
thin film manufacturing techniques as described above are generally
less complex and more reliable. cost effective, and robust,
especially compared with the power and thermal requirements and
labor intensive aspects of piezoelectric device production and with
the complex, expensive, and low-yield surface or bulk
micromachining operations used in for silicon MEMS-based
approaches. Such manufacturing difficulties tend to increase for
parallel plate structures due to the tight tolerances on parallel
orientation, on the order of tens of nanometers for high
performance.
The exemplary implementations described above employ optical
cavities with specific parameters and modes, but a wide variety of
cavities could be used. Cavities with widths in the range from a
few .mu.m to hundreds of .mu.m are feasible, and photon energies
ranging from the ultraviolet up to the far infrared could be
sampled.
In addition, components could have various shapes, dimensions, or
other numerical or qualitative characteristics other than those
illustrated and described above. For example, in some exemplary
implementations described above, cells of a photosensor array
photosense in different subranges of an application's photon energy
range. The subranges of cells could have any appropriate widths and
relationships, and could, for example, overlap or be distinct. The
width of a cell's subrange can be chosen by designing an optical
cavity and the cell sensing area; for example, the width may be as
small as 0.1 nm or as great as tens of nanometers.
Some of the above exemplary implementations involve specific
materials, such as in deformable components such as spacers, in
signal-responsive components such as electrodes, in photosensor
arrays or position-sensitive detectors, and in components that
provide optical cavities such as mirrors, but the invention could
be implemented with a wide variety of materials and with layered
structures with various combinations of sublayers. In particular,
photosensor arrays for a desired speed, sensitivity and wavelength
range could have any suitable material, such as silicon, germanium,
indium-gallium-arsenide, gallium arsenide, gallium nitride, or lead
sulphide, and could be produced with any appropriate kind of
devices, including, for example, photodiodes, avalanche
photodiodes, p-i-n diodes, photoconductors, and so forth, with any
appropriate technique for sensing and reading out information
whether based on CCD, CMOS, or other techniques. Various
commercially available detector arrays have pixel densities as high
as ten megapixels, and some high density ICs have become relatively
inexpensive.
Similarly, optical cavities and related components could be
fabricated with any appropriate techniques, including thin film
technology such as sputtering, e-beam or thermal evaporation with
or without plasma assistance, epitaxial growth, MBE, MOCVD, and so
forth. To produce Bragg mirrors, appropriate pairs of materials
with low absorption coefficients and large difference in refractive
indices could be chosen, bearing in mind the photon energies of
interest; exemplary materials include SiO.sub.2/TiO.sub.2,
SiO.sub.2/Ta.sub.2O.sub.5, GaAs/AlAs, and GaAs/AlGaAs. Thicknesses
of layer in optical cavities may vary from 30 nm up to a few
hundred nanometers.
Some of the above exemplary implementations could involve
particular types of optical cavity structures, such as Bragg
mirrors and paired distributed Bragg reflectors separated by a
Fabry-Perot cavity, but, more generally, any appropriate optical
cavity structure could be used to produce a laterally varying
energy distribution.
Some of the above exemplary implementations use specific lasers or
other light sources to obtain light with desired characteristics,
but various other light source techniques could be used within the
scope of the invention. Various propagation components that
propagate light between other components could also be
employed.
The exemplary implementation in FIGS. 8 and 9 employs a CPU, which
could be a microprocessor or any other appropriate component.
Furthermore, as noted above, adjustment, combining, and other
operations on photosensed quantities could be done either digitally
or with analog signals, and could be done either on the same IC as
a photosensor array, on other components, or on a combination of
the two, with any appropriate combination of software or
hardware.
The above exemplary implementations generally involve production
and/or use of ICs and other photosensing components, optical
cavities, deformable components such as spacers, signal-responsive
components such as electrodes, light sources, processing circuitry,
and control circuitry following particular operations, but
different operations could be performed, the order of the
operations could be modified, and additional operations could be
added within the scope of the invention. For example, readout of
adjusted or unadjusted photosensed quantities from an IC could be
performed serially or in parallel, and could be performed
cell-by-cell or in a streaming operation.
While the invention has been described in conjunction with specific
exemplary implementations, it is evident to those skilled in the
art that many alternatives, modifications, and variations will be
apparent in light of the foregoing description. Accordingly, the
invention is intended to embrace all other such alternatives,
modifications, and variations that fall within the spirit and scope
of the appended claims.
* * * * *
References